Precoding matrix indication method, communications apparatus, and storage medium

ABSTRACT

Embodiments of this application provide a precoding matrix indication method, a communications apparatus, and a storage medium. A precoding matrix of each of K frequency-domain units satisfies W=W 1 ×W 2 , and elements in W 2  in the K frequency-domain units are represented by P elements that are relatively few. A terminal device reports third indication information, where the third indication information includes first indication information and the second indication information, and the first indication information and the second indication information are independently encoded. The first indication information is used to indicate the P elements, and the second indication information is used to indicate P. Therefore, the terminal device can adjust a quantity of information bits of the second indication information based on a channel condition change, thereby improving precoding matrix reporting efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/214,175, filed on Mar. 26, 2021, which is a continuation ofInternational Application No. PCT/CN2018/108480, filed on Sep. 28, 2018.All of the aforementioned patent applications are hereby incorporated byreference in their entireties.

TECHNICAL FIELD

This application relates to the field of communications technologies,and in particular, to a precoding matrix indication method, acommunications apparatus, and a storage medium.

BACKGROUND

In a long term evolution (LTE) system, a base station device receiveschannel state information (CSI) reported by a terminal device. The CSIincludes a precoding matrix indicator PMI, and the PMI is used toindicate, to the base station device, a channel precoding matrix (PM)selected by the terminal device. The base station device generates aprecoding matrix according to the PMI, and sends downlink data on anantenna of the base station device by using the precoding matrix.

The terminal device reports the CSI to the base station device, wherethe CSI is divided into two parts: a first part, part 1 CSI and a secondpart, part 2 CSI. The part 1 CSI includes a rank indicator (RI), achannel quality indicator (CQI) of a first codeword, and a quantity ofnon-zero wideband amplitude coefficients in W₂. The part 2 CSI is usedto report indication information of W₁, and sub-band amplitudescorresponding to a wideband amplitude and a non-zero wideband amplitudein W₂, and a sub-band phase corresponding to the non-zero widebandamplitude in W₂. In addition, the part 1 CSI and the part 2 CSI areindependently encoded. In the CSI reported by the terminal device, aquantity of bits in the part 1 CSI is fixed, a quantity of bits in thepart 2 CSI is variable, and the quantity of bits in the part 2 CSI canbe determined based on the RI and the quantity of non-zero widebandamplitude coefficients in W₂ in the part 1 CSI. A base station maydemodulate information bits of the part 2 CSI based on information inthe part 1 CSI.

However, in a CSI compression technology, the terminal device performsreporting after performing secondary filtering on coefficients in eachW₂. Therefore, through an existing CSI reporting manner, the quantity ofbits in the part 2 CSI cannot be determined based on the quantity ofnon-zero wideband amplitude coefficients in W₂ reported in the part 1CSI, so that the base station cannot demodulate the information bits ofthe part 2 CSI based on the information in the part 1 CSI, therebyaffecting data transmission.

SUMMARY

This application provides a precoding matrix indication method, acommunications apparatus, and a storage medium, to report necessarydemodulation information in a precoding matrix to avoid abnormal datatransmission.

According to a first aspect, this application provides a precodingmatrix indication method. The method includes: A terminal devicegenerates third indication information, where the third indicationinformation is used to indicate W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)),where W^((k)) is a precoding matrix in a k^(th) frequency-domain unit,W^((k)) satisfies W^((k))=W₁×W₂ ^((k)), W₁ is an N_(t)×L matrix, W₂^((k)) is an L×R matrix, 0<k≤K, and K is a quantity of frequency-domainunits; the third indication information includes second indicationinformation and first indication information; the second indicationinformation is used to indicate P_(i,j) elements in a vector D_(i,j),where the vector D_(i,j) and a matrix F_(i,j) satisfyV_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j) corresponds to W₂ ⁽¹⁾(i,j),W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), W₂ ^((k))(i,j) is a complexnumber in an i^(th) row and a j^(th) column of the matrix W₂ ^((k)), andF_(i,j) is a K×P_(i,j) matrix, where 0<i≤L, 0<j≤R, and P_(i,j)<K; andthe first indication information is used to indicate a quantity of theelements indicated by the second indication information; and theterminal device sends the third indication information.

According to the solution provided in this embodiment, a quantity ofelements reported in the precoding matrix is reported, so that a networkdevice that receives the third indication information can decode CSIbased on the information, and the terminal device can dynamically adjustthe quantity of the reported elements based on a channel condition. Thisreduces resource overheads required for CSI reporting.

In a possible design, that the vector V_(i,j) corresponds to W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) includes: V_(i,j) is acolumn vector including W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j); or V_(i,j) is a column vector including amplitudes of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j); or V_(i,j) is acolumn vector including phases of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , andW₂ ^((K))(i,j). The vector V_(i,j) may be represented asV_(i,j)=[α_(i,j) ¹ . . . α_(i,j) ^(K)]^(T), where α_(i,j) ^(k) is W₂^((k))(i,j), or an amplitude of W₂ ^((k))(i,j), or a phase of W₂^((k))(i,j).

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(i,j) or P_(i,j)−1, and(i,j)∈S, where S is a nonempty subset of a set {(x,y)|(x∈{1,2, . . . ,L}, y∈{1,2, . . . , R})}.

The set S represents value ranges of i and j in the vector D_(i,j) thatneeds to be reported by the terminal device. It should be noted thateach matrix of the matrices W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)) is amatrix with L rows and R columns. However, in the K L×R matrices,amplitudes of some elements are 0, and the terminal device may notreport D_(i,j) corresponding to the element whose amplitude is 0.Therefore, values of i and j are a nonempty subset of the set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. A value set of (x,y)in {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}) is (1,1), (1,2), .. . , (1,R), (2,1), (2,2), . . . , (2,R), . . . , (L,1), (L,2), . . . ,and (L,R).

According to the solution provided in this embodiment, a quantity ofelements in each vector D_(i,j) is reported, so that the quantity of thereported elements in the precoding matrix is indicated, thereby avoidingabnormal data transmission.

In a possible design, the quantity of the elements indicated by thesecond indication information includes: Σ_((i,j)∈S)P_(i,j) orΣ_((i,j)∈S)(P_(i,j)−1), where S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. According to the solutionprovided in this embodiment, a total quantity of the reported elementsin the precoding matrix is directly indicated, so that an amount of datareported by the terminal device can be reduced on a basis that thenetwork device can demodulate the CSI.

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(q), where P_(q) is a sum ofthe quantity P_(i,j) of the elements when j=q is given:P_(q)=Σ_(j=q and (i,j)∈S)P_(i,j) orP_(q)=Σ_(j=q and (i,j)∈S)(P_(i,j)−1), and S is a nonempty subset of aset {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. In the solution provided inthis embodiment, each j corresponds to a layer of the precoding matrix,so that the solution is used by the terminal device to report a quantityof reported elements corresponding to each layer. This hierarchicalreporting manner helps improve a CSI demodulation rate of the networkdevice.

In a possible design, the P_(i,j) elements in the vector D_(i,j) areP_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j) elements inthe vector D_(i,j); or the P_(i,j) elements in the vector D_(i,j) arephases of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain the phases of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j)elements in the vector D_(i,j); or the P_(i,j) elements in the vectorD_(i,j) are amplitudes of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j),. . . , and W₂ ^((K))(i,j), and the matrix F_(i,j) is used to obtain theamplitudes of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) basedon the P_(i,j) elements in the vector D_(i,j).

In this case, the method further includes: The terminal device sendsfourth indication information, where the fourth indication informationis used to indicate frequency-domain positions of the P_(i,j) elementsin W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) that correspondto the P_(i,j) elements in the vector D_(i,j).

According to the solution provided in this embodiment, not allcoefficients in W₂ ^((k)) need to be reported, and only an element at aninflection point that can represent a frequency-domain position of W₂^((k)) needs to be reported, thereby greatly reducing an amount of datareported by the terminal device.

In another possible design, P_(i,j) vectors of the matrix F_(i,j) areorthogonal to each other.

In this case, the method further includes: The terminal device sendsfifth indication information, where the fifth indication information isused to indicate the matrix F_(i,j).

According to the solution provided in this embodiment, matrixtransformation may be performed on coefficients in frequency domain, anda limited quantity of sample points with a relatively large value areselected, from results obtained after the matrix transformation, forreporting. In this way, the amount of data reported by the terminaldevice is reduced.

In another possible design, the method further includes: The terminaldevice sends sixth indication information, where the sixth indicationinformation is used to indicate a quantity of the vectors D_(i,j), where(i,j)∈S or (i,j)∈S and j=q are satisfied, and S is a nonempty subset ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. The meaning ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})} is described inthe foregoing paragraph.

In another possible design, the first indication information includesone or more bitmaps; and each bitmap is used to indicate positions ofthe P_(i,j) elements in the vector D_(i,j).

In this embodiment, the first indication information includes onebitmap, so that the bitmap is used to indicate position information ofelements in all reported vectors D_(i,j) in K positions. Alternatively,the first indication information includes R bitmaps, and the bitmaps areused to indicate position information, in K positions, of elements invectors D_(i,j) whose value of j is 1, 2, . . . , or R in all reportedvectors D_(i,j). Alternatively, the first indication informationincludes L×R or (L−1)×R bitmaps, and the bitmaps are used to indicateposition information, in K positions, of an element that is in D_(i,j)and that corresponds to each element in W₂ or each element other than anelement corresponding to a largest amplitude in each column of W₂.

According to the solution provided in this embodiment, when the quantityof the reported elements is indicated, a position of the reportedelement may be indicated, and the position of the reported element doesnot need to be indicated in another manner. This manner has relativelyhigh flexibility and scalability.

In another possible design, the third indication information is channelstate information CSI, and the CSI includes: a first part, part 1 CSI,including the first indication information, a rank indicator RI, and achannel quality indicator CQI that corresponds to a first codeword; anda second part, part 2 CSI, including the second indication information,where the part 1 CSI and the part 2 CSI are independently encoded. Inthis way, the part 1 CSI may indicate a quantity of bits in the part 2CSI, so that the network device that receives the third indicationinformation can decode the CSI based on the information, therebyavoiding abnormal data transmission.

According to a second aspect, this application provides a precodingmatrix indication method. The method includes: A network device receivesthird indication information, where the third indication information isused to indicate W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)), where W^((k)) isa precoding matrix in a k^(th) frequency-domain unit, W^((k)) satisfiesW^((k))=W₁×W₂ ^((k)), W₁ is an N_(t)×L matrix, W₂ ^((k)) is an L×Rmatrix, 0<k≤K, and K is a quantity of frequency-domain units; the thirdindication information includes second indication information and firstindication information; the second indication information is used toindicate P_(i,j) elements in a vector D_(i,j), where the vector D_(i,j)and a matrix F_(i,j) satisfy V_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j)corresponds to W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) W₂^((k))(i,j) is a complex number in an i^(th) row and a j^(th) column ofthe matrix W₂ ^((k)), and F_(i,j) is a K×P_(i,j) matrix, where 0<i≤L,0<j≤R, and P_(i,j)<K; and the first indication information is used toindicate a quantity of the elements indicated by the second indicationinformation; and the network device sends downlink data based on thethird indication information.

According to the solution provided in this embodiment, a quantity ofelements reported in the precoding matrix is reported, so that thenetwork device that receives the third indication information can decodeCSI based on the information, and a terminal device can dynamicallyadjust the quantity of the reported elements based on a channelcondition. This reduces resource overheads required for CSI reporting.

In a possible design, that the vector V_(i,j) corresponds to W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) includes: V_(i,j) is acolumn vector including W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j); or V_(i,j) is a column vector including amplitudes of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . and W₂ ^((K))(i,j); or V_(i,j) is a columnvector including phases of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j). The vector V_(i,j) may be represented as V_(i,j)=[α_(i,j) ¹. . . α_(i,j) ^(K)]^(T), where α_(i,j) ^(k) is W₂ ^((k))(i,j), or anamplitude of W₂ ^((k))(i,j), or a phase of W₂ ^((k))(i,j).

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(i,j) or P_(i,j)−1, and(i,j)∈S, where S is a nonempty subset of a set {(x,y)|(x∈{1,2, . . . ,L}, y∈{1,2, . . . , R})}.

The set S represents value ranges of i and j in the vector D_(i,j) thatneeds to be reported by the terminal device. It should be noted thateach matrix of the matrices W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)) is amatrix with L rows and R columns. However, in the K L×R matrices,amplitudes of some elements are 0, and the terminal device may notreport D_(i,j) corresponding to the element whose amplitude is 0.Therefore, values of i and j are a nonempty subset of the set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. A value set of (x,y)in {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}) is (1,1), (1,2), .. . , (1,R), (2,1), (2,2), . . . , (2,R), . . . , (L,1), (L,2), . . . ,and (L,R).

According to the solution provided in this embodiment, a quantity ofelements in each vector D_(i,j) is reported, so that the quantity of thereported elements in the precoding matrix is indicated, thereby avoidingabnormal data transmission.

In a possible design, the quantity of the elements indicated by thesecond indication information includes: Σ_((i,j)∈S)P_(i,j) orΣ_((i,j)∈S)(P_(i,j)−1), where S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. According to the solutionprovided in this embodiment, a total quantity of the reported elementsin the precoding matrix is directly indicated, so that an amount of datareported by the terminal device can be reduced on a basis that thenetwork device can demodulate the CSI.

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(q), where P_(q) is a sum ofthe quantity P_(i,j) of the elements when j=q is given:P_(q)=_(j=q and (i,j)∈S)P_(i,j) or P_(q)=Σ_(j=q and (i,j)∈S)(P_(i,j)−1),and S is a nonempty subset of a set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2,. . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. In the solution provided inthis embodiment, each j corresponds to a layer of the precoding matrix,so that the solution is used by the terminal device to report a quantityof reported elements corresponding to each layer. This hierarchicalreporting manner helps improve a CSI demodulation rate of the networkdevice.

In a possible design, the P_(i,j) elements in the vector D_(i,j) areP_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j) elements inthe vector D_(i,j); or the P_(i,j) elements in the vector D_(i,j) arephases of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain the phases of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j)elements in the vector D_(i,j); or the P_(i,j) elements in the vectorD_(i,j) are amplitudes of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j),. . . , and W₂ ^((K))(i,j), and the matrix F_(i,j) is used to obtain theamplitudes of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) basedon the P_(i,j) elements in the vector D_(i,j).

In this case, the method further includes: The network device receivesfourth indication information, where the fourth indication informationis used to indicate frequency-domain positions of the P_(i,j) elementsin W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) that correspondto the P_(i,j) elements in the vector D_(i,j).

According to the solution provided in this embodiment, not allcoefficients in W₂ ^((k)) need to be reported, and only an element at aninflection point that can represent a frequency-domain position of W₂^((k)) needs to be reported, thereby greatly reducing an amount of datareported by the terminal device.

In another possible design, P_(i,j) vectors of the matrix F_(i,j) areorthogonal to each other.

In this case, the method further includes: The network device receivesfifth indication information, where the fifth indication information isused to indicate the matrix F_(i,j).

According to the solution provided in this embodiment, matrixtransformation may be performed on coefficients in frequency domain, anda limited quantity of sample points with a relatively large value areselected, from results obtained after the matrix transformation, forreporting. In this way, the amount of data reported by the terminaldevice is reduced.

In another possible design, the method further includes: The networkdevice receives sixth indication information, where the sixth indicationinformation is used to indicate a quantity of the vectors D_(i,j), where(i,j)∈S or (i,j)∈S and j=q are satisfied, and S is a nonempty subset ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. The meaning ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})} is described inthe foregoing paragraph.

In another possible design, the first indication information includesone or more bitmaps; and each bitmap is used to indicate positions ofthe P_(i,j) elements in the vector D_(i,j).

In this embodiment, the first indication information includes onebitmap, so that the bitmap is used to indicate position information ofelements in all reported vectors D_(i,j) in K positions. Alternatively,the first indication information includes R bitmaps, and the bitmaps areused to indicate position information, in K positions, of elements invectors D_(i,j) whose value of j is 1,2, . . . , or R in all reportedvectors D_(i,j). Alternatively, the first indication informationincludes L×R or (L−1)×R bitmaps, and the bitmaps are used to indicateposition information, in K positions, of an element that is in D_(i,j)and that corresponds to each element in W₂ or each element other than anelement corresponding to a largest amplitude in each column of W₂.

According to the solution provided in this embodiment, when the quantityof the reported elements is indicated, a position of the reportedelement may be indicated, and the position of the reported element doesnot need to be indicated in another manner. This manner has relativelyhigh flexibility and scalability.

In another possible design, the third indication information is channelstate information CSI, and the CSI includes: a first part, part 1 CSI,including the first indication information, a rank indicator RI, and achannel quality indicator CQI that corresponds to a first codeword; anda second part, part 2 CSI, including the second indication information,where the part 1 CSI and the part 2 CSI are independently encoded. Inthis way, the part 1 CSI may indicate a quantity of bits in the part 2CSI, so that the network device that receives the third indicationinformation can decode the CSI based on the information, therebyavoiding abnormal data transmission.

According to a third aspect, this application provides a communicationsapparatus, including a processing module and a sending module. Theprocessing module is configured to generate third indicationinformation, where the third indication information is used to indicateW₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)) where W^((k)) is a precodingmatrix in a k^(th) frequency-domain unit, W^((k)) satisfiesW^((k))=W₁×W₂ ^((k)), W₁ is an N_(t)×L matrix, W₂ ^((k)) is an L×Rmatrix, 0<k≤K, and K is a quantity of frequency-domain units; the thirdindication information includes second indication information and firstindication information; the second indication information is used toindicate P_(i,j) elements in a vector D_(i,j), where the vector D_(i,j)and a matrix F_(i,j) satisfy V_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j)corresponds to W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), W₂^((k))(i,j) is a complex number in an i^(th) row and a j^(th) column ofthe matrix W₂ ^((k)), and F_(i,j) is a K×P_(i,j) matrix, where 0<i≤L,0<j≤R, and P_(i,j)<K; and the first indication information is used toindicate a quantity of the elements indicated by the second indicationinformation; and the sending module is configured to send the thirdindication information.

According to the solution provided in this embodiment, a quantity ofelements reported in the precoding matrix is reported, so that a networkdevice that receives the third indication information can decode CSIbased on the information, and a terminal device can dynamically adjustthe quantity of the reported elements based on a channel condition. Thisreduces resource overheads required for CSI reporting.

In a possible design, that the vector V_(i,j) corresponds to W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j) . . . , and W₂ ^((K))(i,j) includes: V_(i,j) is acolumn vector including W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j); or V_(i,j) is a column vector including amplitudes of W₂⁽¹⁾(i,j), W₂) (i,j), and W₂ ^((K))(i,j); or V_(i,j) is a column vectorincluding phases of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j). The vector V_(i,j) may be represented as V_(i,j)=[α_(i,j) ¹. . . α_(i,j) ^(K)]^(T), where α_(i,j) ^(k) is W₂ ^((k))(i,j), or anamplitude of W₂ ^((k))(i,j), or a phase of W₂ ^((k))(i,j).

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(i,j) or P_(i,j)−1, and(i,j)∈S, where S is a nonempty subset of a set {(x,y)|(x∈{1,2, . . . ,L}, y∈{1,2, . . . , R})}.

The set S represents value ranges of i and j in the vector D_(i,j) thatneeds to be reported by the terminal device. It should be noted thateach matrix of the matrices W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)) is amatrix with L rows and R columns. However, in the K L×R matrices,amplitudes of some elements are 0, and the terminal device may notreport D_(i,j) corresponding to the element whose amplitude is 0.Therefore, values of i and j are a nonempty subset of the set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. A value set of (x,y)in {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}) is (1,1), (1,2), .. . , (1,R), (2,1), (2,2), . . . , (2,R), . . . , (L,1), (L,2), . . . ,and (L,R).

According to the solution provided in this embodiment, a quantity ofelements in each vector D_(i,j) is reported, so that the quantity of thereported elements in the precoding matrix is indicated, thereby avoidingabnormal data transmission.

In a possible design, the quantity of the elements indicated by thesecond indication information includes: Σ_((i,j)∈S)P_(i,j) orΣ_((i,j)∈S)(P_(i,j)−1), where S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. According to the solutionprovided in this embodiment, a total quantity of the reported elementsin the precoding matrix is directly indicated, so that an amount of datareported by the terminal device can be reduced on a basis that thenetwork device can demodulate the CSI.

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(q), where P_(q) is a sum ofthe quantity P_(i,j) of the elements when j=q is given:P_(q)=Σ_(j=q and (i,j)∈S)P_(i,j) orP_(q)=Σ_(j=q and (i,j)∈S)(P_(i,j)−1), and S is a nonempty subset of aset {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. In the solution provided inthis embodiment, each j corresponds to a layer of the precoding matrix,so that the solution is used by the terminal device to report a quantityof reported elements corresponding to each layer. This hierarchicalreporting manner helps improve a CSI demodulation rate of the networkdevice.

In a possible design, the P_(i,j) elements in the vector D_(i,j) areP_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾((i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j) elements inthe vector D_(i,j); or the P_(i,j) elements in the vector D_(i,j) arephases of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain the phases of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j)elements in the vector D_(i,j); or the P_(i,j) elements in the vectorD_(i,j) are amplitudes of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j),. . . , and W₂ ^((K))(i,j), and the matrix F_(i,j) is used to obtain theamplitudes of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) basedon the P_(i,j) elements in the vector D_(i,j).

In this case, the sending module is further configured to send fourthindication information, where the fourth indication information is usedto indicate frequency-domain positions of the P_(i,j) elements in W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) that correspond to theP_(i,j) elements in the vector D_(i,j).

According to the solution provided in this embodiment, not allcoefficients in W₂ ^((k)) need to be reported, and only an element at aninflection point that can represent a frequency-domain position of W₂^((k)) needs to be reported, thereby greatly reducing an amount of datareported by the terminal device.

In another possible design, P_(i,j) vectors of the matrix F_(i,j) areorthogonal to each other.

In this case, the sending module is further configured to send fifthindication information, where the fifth indication information is usedto indicate the matrix F_(i,j).

According to the solution provided in this embodiment, matrixtransformation may be performed on coefficients in frequency domain, anda limited quantity of sample points with a relatively large value areselected, from results obtained after the matrix transformation, forreporting. In this way, the amount of data reported by the terminaldevice is reduced.

In another possible design, the sending module is further configured tosend sixth indication information, where the sixth indicationinformation is used to indicate a quantity of the vectors D_(i,j), where(i,j)∈S or i,j satisfy (i,j)∈S and j=k, and S is a nonempty subset ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. The meaning ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})} is described inthe foregoing paragraph.

In another possible design, the first indication information includesone or more bitmaps; and each bitmap is used to indicate positions ofthe P_(i,j) elements in the vector D_(i,j).

In this embodiment, the first indication information includes onebitmap, so that the bitmap is used to indicate position information ofelements in all reported vectors D_(i,j) in K positions. Alternatively,the first indication information includes R bitmaps, and the bitmaps areused to indicate position information, in K positions, of elements invectors D_(i,j) whose value of j is 1,2, . . . , or R in all reportedvectors D_(i,j). Alternatively, the first indication informationincludes L×R or (L−1)×R bitmaps, and the bitmaps are used to indicateposition information, in K positions, of an element that is in D_(i,j)and that corresponds to each element in W₂ or each element other than anelement corresponding to a largest amplitude in each column of W₂.

According to the solution provided in this embodiment, when the quantityof the reported elements is indicated, a position of the reportedelement may be indicated, and the position of the reported element doesnot need to be indicated in another manner. This manner has relativelyhigh flexibility and scalability.

In another possible design, the third indication information is channelstate information CSI, and the CSI includes: a first part, part 1 CSI,including the first indication information, a rank indicator RI, and achannel quality indicator CQI that corresponds to a first codeword; anda second part, part 2 CSI, including the second indication information,where the part 1 CSI and the part 2 CSI are independently encoded. Inthis way, the part 1 CSI may indicate a quantity of bits in the part 2CSI, so that the network device that receives the third indicationinformation can decode the CSI based on the information, therebyavoiding abnormal data transmission.

According to a fourth aspect, this application provides a communicationsapparatus, including a receiving module and a processing module. Thereceiving module is configured to receive third indication information,where the third indication information is used to indicate W₂ ⁽¹⁾, W₂⁽²⁾, . . . , and W₂ ^((K)) where W^((k)) is a precoding matrix in ak^(th) frequency-domain unit, W^((k)) satisfies W^((k))=W₁×W^((k)), W₁is an N_(t)×L matrix, W₂ ^((k)) is an L×R matrix, 0<k≤K, and K is aquantity of frequency-domain units; the third indication informationincludes second indication information and first indication information;the second indication information is used to indicate P_(i,j) elementsin a vector D_(i,j), where the vector D_(i,j) and a matrix F_(i,j)satisfy V_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j) corresponds to W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), W₂ ^((k))(i,j) is acomplex number in an i^(th) row and a j^(th) column of the matrix W₂^((k)), and F_(i,j) is a K×P_(i,j) matrix, where 0<i≤L, 0<j≤R, andP_(i,j)<K; and the first indication information is used to indicate aquantity of the elements indicated by the second indication information;and the processing module is configured to send downlink data based onthe third indication information.

According to the solution provided in this embodiment, a quantity ofelements reported in the precoding matrix is reported, so that a networkdevice that receives the third indication information can decode CSIbased on the information, and a terminal device can dynamically adjustthe quantity of the reported elements based on a channel condition. Thisreduces resource overheads required for CSI reporting.

In a possible design, that the vector V_(i,j) corresponds to W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) includes: V_(i,j) is acolumn vector including W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j); or V_(i,j) is a column vector including amplitudes of W₂⁽¹⁾(i,j) W₂ ⁽²⁾(i,j), . . . and W₂ ^((K))(i,j); or V_(i,j) is a columnvector including phases of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((k))(i,j). The vector V_(i,j) may be represented as V_(i,j)=[α_(i,j) ¹. . . α_(i,j) ^(K)]^(T), where α_(i,j) ^(k) is W₂ ^((k))(i,j), or anamplitude of W₂ ^((k))(i,j), or a phase of W₂ ^((k))(i,j).

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(i,j) or P_(i,j)−1, and(i,j)∈S, where S is a nonempty subset of a set {(x,y)|(x∈{1,2, . . . ,L}, y∈{1,2, . . . , R})}.

The set S represents value ranges of i and j in the vector D_(i,j) thatneeds to be reported by the terminal device. It should be noted thateach matrix of the matrices W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)) is amatrix with L rows and R columns. However, in the K L×R matrices,amplitudes of some elements are 0, and the terminal device may notreport D_(i,j) corresponding to the element whose amplitude is 0.Therefore, values of i and j are a nonempty subset of the set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. A value set of (x,y)in {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}) is (1,1), (1,2), .. . , (1,R), (2,1), (2,2), . . . , (2,R), . . . , (L,1), (L,2), . . . ,and (L,R).

According to the solution provided in this embodiment, a quantity ofelements in each vector D_(i,j) is reported, so that the quantity of thereported elements in the precoding matrix is indicated, thereby avoidingabnormal data transmission.

In a possible design, the quantity of the elements indicated by thesecond indication information includes: Σ_((i,j)∈S)P_(i,j) orΣ_((i,j)∈S)(P_(i,j)−1), where S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. According to the solutionprovided in this embodiment, a total quantity of the reported elementsin the precoding matrix is directly indicated, so that an amount of datareported by the terminal device can be reduced on a basis that thenetwork device can demodulate the CSI.

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(q), where P_(q) is a sum ofthe quantity P_(i,j) of the elements when j=q is given:P_(q)=Σ_(j=q and (i,j)∈S)P_(i,j) orP_(q)=>Σ_(j=q and (i,j)∈S)(P_(i,j)−1), and S is a nonempty subset of aset {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. In the solution provided inthis embodiment, each j corresponds to a layer of the precoding matrix,so that the solution is used by the terminal device to report a quantityof reported elements corresponding to each layer. This hierarchicalreporting manner helps improve a CSI demodulation rate of the networkdevice.

In a possible design, the P_(i,j) elements in the vector D_(i,j) areP_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain W₂ ⁽¹⁾(i,j), W₂⁽¹⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j) elements inthe vector D_(i,j); or the P_(i,j) elements in the vector D_(i,j) arephases of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain the phases of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j)elements in the vector D_(i,j); or the P_(i,j) elements in the vectorD_(i,j) are amplitudes of P_(i,j) elements in W₂ ^((i,j))(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), and the matrix F_(i,j) is used toobtain the amplitudes of W₂ ^((i,j))(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j) based on the P_(i,j) elements in the vector D_(i,j).

In this case, the receiving module is further configured to receivefourth indication information, where the fourth indication informationis used to indicate frequency-domain positions of the P_(i,j) elementsin W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) that correspondto the P_(i,j) elements in the vector D_(i,j).

According to the solution provided in this embodiment, not allcoefficients in W₂ ^((k)) need to be reported, and only an element at aninflection point that can represent a frequency-domain position of W₂^((k)) needs to be reported, thereby greatly reducing an amount of datareported by the terminal device.

In another possible design, P_(i,j) vectors of the matrix F_(i,j) areorthogonal to each other.

In this case, the receiving module is further configured to receivefifth indication information, where the fifth indication information isused to indicate the matrix F_(i,j).

According to the solution provided in this embodiment, matrixtransformation may be performed on coefficients in frequency domain, anda limited quantity of sample points with a relatively large value areselected, from results obtained after the matrix transformation, forreporting. In this way, the amount of data reported by the terminaldevice is reduced.

In another possible design, the receiving module is further configuredto receive sixth indication information, where the sixth indicationinformation is used to indicate a quantity of the vectors D_(i,j), where(i,j)∈S or (i,j)∈S and j=q are satisfied, and S is a nonempty subset ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. The meaning ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})} is described inthe foregoing paragraph.

In another possible design, the first indication information includesone or more bitmaps; and each bitmap is used to indicate positions ofthe P_(i,j) elements in the vector D_(i,j).

In this embodiment, the first indication information includes onebitmap, so that the bitmap is used to indicate position information ofelements in all reported vectors D_(i,j) in K positions. Alternatively,the first indication information includes R bitmaps, and the bitmaps areused to indicate position information, in K positions, of elements invectors D_(i,j) whose value of j is 1, 2, . . . , or R in all reportedvectors D_(i,j). Alternatively, the first indication informationincludes L×R or (L−1)×R bitmaps, and the bitmaps are used to indicateposition information, in K positions, of an element that is in D_(i,j)and that corresponds to each element in W₂ or each element other than anelement corresponding to a largest amplitude in each column of W₂.

According to the solution provided in this embodiment, when the quantityof the reported elements is indicated, a position of the reportedelement may be indicated, and the position of the reported element doesnot need to be indicated in another manner. This manner has relativelyhigh flexibility and scalability.

In another possible design, the third indication information is channelstate information CSI, and the CSI includes: a first part, part 1 CSI,including the first indication information, a rank indicator RI, and achannel quality indicator CQI that corresponds to a first codeword; anda second part, part 2 CSI, including the second indication information,where the part 1 CSI and the part 2 CSI are independently encoded. Inthis way, the part 1 CSI may indicate a quantity of bits in the part 2CSI, so that the network device that receives the third indicationinformation can decode the CSI based on the information, therebyavoiding abnormal data transmission.

According to a fifth aspect, this application provides a communicationsapparatus, including a transceiver, a processor, a memory, and a bus.The transceiver, the processor, and the memory are connected to the bus,the memory stores program instructions, and the processor runs theprogram instructions to perform the method according to the first aspector the second aspect.

According to a sixth aspect, this application provides acomputer-readable storage medium. The computer-readable storage mediumstores a computer program, and when the computer program is run on acomputer, the computer is enabled to perform the method according to thefirst aspect or the second aspect.

According to a seventh aspect, this application provides a computerprogram product including instructions. When the instructions are run ona computer, the computer is enabled to perform the method according tothe first aspect or the second aspect.

In a possible design, all or some of programs in the seventh aspect maybe stored in a storage medium encapsulated with a processor, or some orall of programs may be stored in a memory that is not encapsulated witha processor.

It can be learned that in the foregoing aspects, the third indicationinformation is generated, so that the quantity of the reported elementsindicated by the second indication information is obtained through thefirst indication information in the third indication information. Afterreceiving the third indication information, the network device candemodulate the part 2 CSI based on the quantity indicated by the firstindication information, so that normal data transmission can beimplemented.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an application scenario according to anembodiment of this application;

FIG. 2 is a schematic flowchart of a precoding matrix indication methodaccording to this application;

FIG. 3 is a curve of a frequency-domain relationship between a phase anda sub-band number of each vector D_(i,j) according to this application;

FIG. 4 is a curve of a time-domain relationship obtained after IDFTtransform is performed on coefficients in W₂ ^((k)) according to thisapplication;

FIG. 5 is a schematic interaction flowchart of a precoding matrixindication method according to this application;

FIG. 6 is a structural block diagram of a communications apparatusaccording to this application;

FIG. 7 is a schematic structural diagram of another communicationsapparatus according to this application;

FIG. 8 is a schematic structural diagram of another communicationsapparatus according to this application;

FIG. 9 is a schematic structural diagram of another communicationsapparatus according to this application;

FIG. 10 is a schematic structural diagram of another communicationsapparatus according to this application; and

FIG. 11 is a schematic structural diagram of another communicationsapparatus according to this application.

DESCRIPTION OF EMBODIMENTS

Terms used in implementations of this application are merely used toexplain specific embodiments of this application, but are not intendedto limit this application.

The embodiments of this application may be used in various types ofcommunications systems. FIG. 1 is a schematic diagram of an applicationscenario according to an embodiment of this application. As shown inFIG. 1 , a communications system mainly includes a network device 11 anda terminal device 12.

(1) The network device 11 may be a network side device, for example, awireless-fidelity (Wi-Fi) access point AP, a next-generationcommunications base station such as a gNB, a small cell, and a microcell of 5G, or a transmission reception point (TRP), or may be a relaystation, an access point, a vehicle-mounted device, a wearable device,or the like. In this embodiment, base stations in communications systemsof different communications standards are different. For distinction, abase station in a 4G communications system is referred to as an LTE eNB,a base station in a 5G communications system is referred to as an NRgNB, and a base station that supports both the 4G communications systemand the 5G communications system is referred to as an eLTE eNB. Thesenames are merely for ease of distinction, and are not intended forlimitation.

(2) The terminal device 12 is also referred to as user equipment (UE) orcustomer premise equipment (CPE), and is a device that provides a userwith voice and/or data connectivity, for example, a handheld device or avehicle-mounted device with a wireless connection function. A commonterminal device includes, for example, a mobile phone, a tablet, anotebook computer, a palmtop computer, a mobile internet device (MID),and a wearable device such as a smartwatch, a smart band, and apedometer.

(3) “A plurality of” means two or more, and another quantifier issimilar to this. The term “and/or” describes a correspondence betweenassociated objects and represents that three relationships may exist.For example, A and/or B may represent the following three cases: Only Aexists, both A and B exist, and only B exists. The character “/”generally indicates an “or” relationship between the associated objects.

In this application, “at least one” means one or more, and “a pluralityof” means two or more than two. The term “and/or” describes anassociation relationship between associated objects and represents thatthree relationships may exist. For example, A and/or B may represent thefollowing cases: Only A exists, both A and B exist, and only B exists,where A and B may be singular or plural. The character “/” generallyindicates an “or” relationship between the associated objects. “At leastone (one piece) of the following” or a similar expression thereof refersto any combination of these items, including any combination of singularitems (piece or plural items (pieces). For example, at least one (onepiece) of a, b, or c may indicate: a, b, c, a-b, a-c, b-c, or a-b-c,where a, b, and c may be singular or plural.

It should be noted that, a quantity and types of terminal devices 12included in the communications system shown in FIG. 1 are merelyexamples, and this embodiment of this application is not limitedthereto. For example, more terminal devices 12 that communicate with thenetwork device 11 may be further included. For brevity, details are notdescribed in the accompanying drawings. In addition, in thecommunications system shown in FIG. 1 , although the network device 11and the terminal device 12 are shown, the communications system mayinclude but is not limited to the network device 11 and the terminaldevice 12, for example, may further include a core network node or adevice configured to carry a virtualized network function. This isobvious to a person skilled in the art, and details are not describedherein.

In addition, the embodiments of this application may be used in not onlya next-generation wireless communications system, that is, the 5Gcommunications system, but also another system that may appear in thefuture, for example, a next-generation Wi-Fi network or a 5G internet ofvehicles.

It should be noted that, with continuous evolution of the communicationssystem, names of network elements in another system that may appear inthe future may change. In this case, the solutions provided in theembodiments of this application are also applicable.

First, a precoding matrix is explained and described in this embodimentof this application. The precoding matrix may be represented as W⁽¹⁾,W⁽²⁾, . . . , and W^((K)), where W^((k)) is a precoding matrix in ak^(th) frequency-domain unit, 0<k≤K, and K is a quantity offrequency-domain units.

The precoding matrix W^((k)) in any (the k^(th)) frequency-domain unitsatisfies W^((k))=W₁×W₂ ^((k)), W₁ is an N_(t)×L matrix, and W₂ ^((k))is an L×R matrix. That is, W^((k)) is an N_(t)×R matrix.

In a possible implementation scenario, a precoding matrix on eachfrequency-domain unit satisfies W=W₁×W₂ (herein, impact of thefrequency-domain unit is ignored, and the superscript (k) is temporarilyomitted during numbering), where W₁ is a diagonal block matrix, eachblock matrix includes L/2 orthogonal two-dimensional discrete Fouriertransform (DFT) vectors, and L is an even number greater than 0. In thiscase, W₁ may be represented as:

$W_{1} = \begin{bmatrix}{b_{1}^{m}\mspace{14mu}\ldots\mspace{14mu} b_{L/2}^{m}} & 0 \\0 & {b_{1}^{m}\mspace{14mu}\ldots\mspace{14mu} b_{L/2}^{m}}\end{bmatrix}$

where b_(l) ^(m) represents a beam vector, l=1, . . . , L/2, and thebeam vectors are orthogonal to each other.

In addition, according to different quantities of ranks (RI),representation forms of W₂ are different. A phase and an amplitude aretwo characteristics of a signal, so that the signal may be describedfrom two angles: the phase and the amplitude. For ease of understanding,this embodiment of this application provides the following tworepresentation forms of W₂.

In a feasible implementation scenario, when a rank is 1, W₂ may berepresented as:

$W_{2} = \begin{bmatrix}{p_{1,1}^{({WB})} \cdot p_{1,1}^{({SB})} \cdot c_{1,1}} \\{p_{2,1}^{({WB})} \cdot p_{2,1}^{({SB})} \cdot c_{2,1}} \\\vdots \\{p_{{L/2},1}^{({WB})} \cdot p_{{L/2},1}^{({SB})} \cdot c_{{L/2},1}} \\{p_{{\frac{L}{2} + 1},1}^{({WB})} \cdot p_{{\frac{L}{2} + 1},1}^{({SB})} \cdot c_{{\frac{L}{2} + 1},1}} \\\vdots \\{p_{L,1}^{({WB})} \cdot p_{L,1}^{({SB})} \cdot c_{L,1}}\end{bmatrix}$

In a feasible implementation scenario, when a rank is 2, W₂ may berepresented as:

$W_{2} = \begin{bmatrix}{p_{1,1}^{({WB})} \cdot p_{1,1}^{({SB})} \cdot c_{1,1}} & {p_{1,2}^{({WB})} \cdot p_{1,2}^{({SB})} \cdot c_{1,2}} \\{p_{2,1}^{({WB})} \cdot p_{2,1}^{({SB})} \cdot c_{2,1}} & {p_{2,2}^{({WB})} \cdot p_{2,2}^{({SB})} \cdot c_{2,2}} \\\vdots & \vdots \\{p_{{L/2},1}^{({WB})} \cdot p_{{L/2},1}^{({SB})} \cdot c_{{L/2},1}} & {p_{{L/2},2}^{({WB})} \cdot p_{{L/2},2}^{({SB})} \cdot c_{{L/2},2}} \\{p_{{\frac{L}{2} + 1},1}^{({WB})} \cdot p_{{\frac{L}{2} + 1},1}^{({SB})} \cdot c_{{\frac{L}{2} + 1},1}} & {p_{{\frac{L}{2} + 1},2}^{({WB})} \cdot p_{{\frac{L}{2} + 1},2}^{({SB})} \cdot c_{{\frac{L}{2} + 1},2}} \\\vdots & \vdots \\{p_{L,1}^{({WB})} \cdot p_{L,1}^{({SB})} \cdot c_{L,1}} & {p_{L,2}^{({WB})} \cdot p_{L,2}^{({SB})} \cdot c_{L,2}}\end{bmatrix}$

where p_(i,j) ^((WB)) represents wideband amplitude information, andp_(i,j) ^((SB)) represents sub-band amplitude information, where p_(i,j)^((WB))∈{1, √{square root over (0.5)}, √{square root over (0.25)},√{square root over (0.125)}, √{square root over (0.0625)}, √{square rootover (0.0313)}, √{square root over (0.0156)}, 0}, p_(i,j)^((SB)∈{)1,√{square root over (0.5)}}, j is a column number of thematrix W₂, and also represents a sequence number of a layer of data, irepresents a row number of the matrix W₂, c_(i,j) represents phaseinformation, and

$c_{i,j} \in {\{ {e^{j\frac{\pi n}{2}},{n = 0},1,2,3} \}\mspace{14mu}{or}\mspace{14mu} c_{i,j}} \in {\{ {e^{j\frac{\pi n}{4}},{n = 0},1,2,{3\mspace{14mu}\ldots}\mspace{14mu},7} \}.}$

Based on the foregoing architecture of the precoding matrix, in theprior art, to reduce a reporting amount as much as possible, a CSIcompression solution is used. Essence of the solution is: For eachcoefficient in each W₂, by using a transform-domain operation, afrequency-domain element that needs to be reported is transformed to atransform domain, and then a limited quantity of large-value samplepoints are selected from elements of the transform domain for reporting,where the transform-domain operation includes, but is not limited to,inverse discrete Fourier transform (IDFT), discrete Fourier transform(DFT), discrete cosine transform (DCT), and inverse discrete cosinetransform (IDCT).

For ease of understanding, this embodiment of this application providesa solution of implementing CSI compression through IDFT transform.Specifically, for any coefficient p_(i,j) ^((WB))·p_(i,j)^((SB))·c_(i,j) in the foregoing W₂, coefficients p_(i,j)^((WB))·p_(i,j) ^((SB))·c_(i,j) of K sub-bands form X_(i,j), andreference are made to Table 1.

TABLE 1 Coefficient Sub-band 1 Sub-band 2 . . . Sub-band K X_(1,1)x_(1,1) ⁽¹⁾ x_(1,1) ⁽²⁾ . . . x_(1,1) ^((K)) X_(2,1) x_(2,1) ⁽¹⁾ x_(2,1)⁽²⁾ . . . x_(2,1) ^((K)) . . . . . . . . . . . . . . . X_(L,R) x_(L,R)⁽¹⁾ x_(L,R) ⁽²⁾ . . . x_(L,R) ^((K))

Then, IDFT transform is performed on each coefficient X_(i,j) in Table 1to obtain Y_(i,j), where Y_(i,j)=IDFT(X_(i,j)). In this case, Table 2shows a representation form of Y_(i,j):

TABLE 2 Transform-domain Time-domain Time-domain Time-domain coefficientsample point 1 sample point 2 . . . sample point K Y_(1,1) y_(1,1) ⁽¹⁾y_(1,1) ⁽²⁾ . . . y_(1,1) ^((K)) Y_(2,1) y_(2,1) ⁽¹⁾ y_(2,1) ⁽²⁾ . . .y_(2,1) ^((K)) . . . . . . . . . . . . . . . Y_(L,R) y_(L,R) ⁽¹⁾ y_(L,R)⁽²⁾ . . . y_(L,R) ^((K))

After the IDFT transform, when performing CSI reporting, the terminaldevice may select a limited quantity of large-value sample points fromeach Y_(i,j) for reporting. Limited quantities of large-value samplepoints selected from all Y_(i,j) may be the same or different, andpositions (a sequence number of a time-domain sample point) of thelimited quantities of large-value sample points selected from allY_(i,j) for reporting may be the same or different.

For example, if in Y_(1,1), values of the time-domain sample point 1 andthe time-domain sample point 2 are relatively large, and values of othertime-domain sample points are relatively small, for Y_(1,1), y_(1,1) ⁽¹⁾and y_(1,1) ⁽²⁾ are reported.

For another example, if in Y_(2,1), a value of a time-domain samplepoint 4 is relatively large, and values of other time-domain samplepoints are relatively small, for the element Y_(2,1), y_(2,1) ⁽⁴⁾ isreported.

In addition, there is another solution for reducing the CSI reportingamount. In each row in Table 1, the terminal device does not need toreport a coefficient x_(i,j) ^((k)) of each sub-band to a base station,where k=1, 2, . . . , K. The terminal device selects P_(i,j)coefficients from K coefficients in each row for reporting. According tothe P_(i,j) coefficients reported by the terminal device and positionsof the P_(i,j) coefficients in the K sub-bands, the base station devicemay obtain a complex coefficient in an i^(th) row and a j^(th) column ofW₂ of the K sub-bands in an interpolation manner.

In a possible interpolation method, linear interpolation is used, thatis, a coefficient

$x_{i,j}^{({k_{1} + n})} = {{\frac{x_{i,j}^{(k_{2})} - x_{i,j}^{(k_{1})}}{k_{2} - k_{1}} \times n} + x_{i,j}^{(k_{1})}}$on a (k₁+n)^(th) sub-band is obtained by using x_(i,j) ^((k) ¹ ⁾ on a k₁^(th) sub-band and x_(i,j) ^((k) ² ⁾ on a k₂ ^(th) sub-band that arereported by the terminal device, where k₁ and k₂ are position indexes oftwo adjacent sub-bands selected by the terminal device, and 0<n<k₂−k₁.

It should be noted that, the P_(i,j) coefficients may be P_(i,j)coefficients x_(i,j) ^((k)), or sub-band phases of P_(i,j) coefficientsx_(i,j) ^((k)), or sub-band amplitudes of P_(i,j) coefficients x_(i,j)^((k)), or include phases of P_(i,j) ¹ coefficients x_(i,j) ^((k)) andamplitudes of P_(i,j) ² coefficients x_(i,j) ^((k)).

In another possible implementation solution, in each row in Table 1, theterminal device reports x_(i,j) ⁽¹⁾ and difference coefficients β_(i,j)⁽²⁾, β_(i,j) ⁽³⁾, . . . , and β_(i,j) ^((P) ^(i,j) ⁾. According tox_(i,j) ⁽¹⁾, β_(i,j) ⁽²⁾, β_(i,j) ⁽³⁾, . . . , and β_(i,j) ^((β) ^(i,j)⁾, and frequency-domain sub-band positions (that is, inflection pointpositions) corresponding to the reported coefficients, the base stationdevice may obtain a complex coefficient in an i^(th) row and a j^(th)column of W₂ of the K sub-bands in an interpolation manner, where n=2,3, . . . , and P_(i,j)−1.

In a possible interpolation method, linear interpolation is used, thatis, a sub-band coefficient between the sub-band 1 and a sub-band k₁ maybe obtained by using x_(i,j) ⁽¹⁾ reported by the terminal device and thesub-band position k₁, for example, x_(i,j) ^((n))=x_(i,j)⁽¹⁾+(n−1)×β_(i,j) ⁽²⁾. Likewise, a sub-band coefficient between thesub-band k₁ and a sub-band k₂ may be obtained according to the obtainedx_(i,j) ^((k) ¹ ⁾ and β_(i,j) ⁽³⁾, for example, x_(i,j) ^((k) ¹^(+n))=x_(i,j) ^((k) ¹ ⁾+(n−1)×β_(i,j) ⁽³⁾. The rest can be deduced byanalogy.

In conclusion, the reporting amount of the terminal device can bereduced by using the CSI compression solution.

In an existing new radio (NR) technology, CSI reported by the terminaldevice includes two parts. A quantity of bits of part 2 CSI can bedetermined based on an RI and a quantity of non-zero wideband amplitudecoefficients in W₁ that are in part 1 CSI, and the base station maydemodulate the part 2 CSI based on information in the part 1 CSI.However, if the CSI compression solution is extended based on the NRtechnology, because a quantity of non-zero elements reported in eachelement Y_(i,j) is different, if an existing precoding matrix indicationmethod is used, the quantity of bits in the part 2 CSI cannot bedetermined based on the RI and the quantity of non-zero widebandamplitude coefficients in W₁ that are reported in the part 1 CSI.Therefore, after the base station receives indication information of theprecoding matrix, it is difficult for the base station to demodulate theindication information, thereby affecting normal data transmission.

The precoding matrix indication method provided in this embodiment ofthis application is provided to resolve the foregoing problem in theprior art.

FIG. 2 shows a precoding matrix indication method according to thisapplication. As shown in FIG. 2 , the method includes the followingsteps.

S202: A terminal device generates third indication information.

The third indication information is used to indicate W₂ ⁽¹⁾, W₂ ⁽²⁾, . .. , and W₂ ^((K)), where W^((k)) is a precoding matrix in a k^(th)frequency-domain unit, W^((k)) satisfies W^((k))=W₁×W₂ ^((k)), W₁ is anN_(t)×L matrix, W₂ ^((k)) is an L×R matrix, 0<k≤K, and K is a quantityof frequency-domain units.

The third indication information includes second indication informationand first indication information.

The second indication information is used to indicate P_(i,j) elementsin a vector D_(i,j), where the vector D_(i,j) and a matrix F_(i,j)satisfy V_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j) corresponds to W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), W₂ ^((k))(i,j) is acomplex number in an i^(th) row and a j^(th) column of the matrix W₂^((k)), and F_(i,j) is a K×P_(i,j) matrix, where 0<i≤L, 0<j≤R, andP_(i,j)<K.

The first indication information is used to indicate a quantity of theelements indicated by the second indication information.

S204: The terminal device sends the third indication information.

The following describes in detail the precoding matrix indication methodshown in FIG. 2 with reference to an embodiment.

According to the precoding matrix indication method provided in thisembodiment of this application, the P_(i,j) elements in the vectorD_(i,j) indicated by the second indication information is a finallyreported limited quantity of elements, and the first indicationinformation indicates the quantity of the elements indicated by thesecond indication information. In this way, through the quantity of theelements indicated by the first indication information, after receivingthe third indication information, a base station may generate theprecoding matrix based on the first indication information and thesecond indication information. In this way, the precoding matrix isindicated.

Further, the precoding matrix indication method provided in thisapplication is applicable to a CSI compression solution, that is, isapplicable to a solution in which only a limited quantity of elementscorresponding to each element are reported during precoding matrixindication. In this case, the third indication information is CSI. TheCSI includes two parts that are independently encoded: part 1 CSI andpart 2 CSI, the first indication information may be carried in the part1 CSI, and the second indication information may be carried in the part2 CSI, so that the base station can demodulate the part 2 CSI, andfurther implement data transmission by using the elements reported inthe second indication information. That is, in this case, the part 1 CSIin the CSI sent by the terminal device may include but is not limited tothe following information: the first indication information, a rankindicator RI, and a channel quality indicator CQI of a first codeword.The part 2 CSI may include but is not limited to the followinginformation: the second indication information and a precoding matrixindicator (PMI). In this way, when the base station receives the CSI,the base station may determine a quantity of bits in the part 2 CSIthrough the first indication information carried in the part 1 CSI.

As described above, in W₂ ^((k)) in a precoding matrix in anyfrequency-domain unit, any coefficient (for example, a coefficient in ani^(th) row and a j^(th) column) may satisfy the following relationship:x_(i,j) ^((k))=p_(i,j) ^((WB)(k))·p_(i,j) ^((SB)(k))·c_(i,j) ^((k)),that is, all coefficients in each W₂ ^((k)) may be represented by awideband amplitude (p_(i,j) ^((WB)(k))), a sub-band amplitude (p_(i,j)^((SB)(k))), and a phase (c_(i,j) ^((k))). In this way, in specificimplementation, that the vector V_(i,j) corresponds to W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), where W₂ ^((k))(i,j)=x_(i,j)^((k)), may include the following cases:

V_(i,j) is a column vector including W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . ,and W₂ ^((K))(i,j); or

V_(i,j) is a column vector including amplitudes of W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K)) (i,j); or

V_(i,j) is a column vector including phases of W₂ ⁽¹⁾(i,j), W₂⁽²⁾((i,j), . . . , and W₂ ^((K))(i,j).

That V_(i,j) is a column vector including amplitudes of W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) may include that V_(i,j) is acolumn vector including wideband amplitudes and/or sub-band amplitudesof W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j).

That is, the vector V_(i,j) may be represented as V_(i,j)=[α_(i,j) ¹ . .. α_(i,j) ^(K)], where α_(i,j) ^(k) is W₂ ^((k))(i,j), or an amplitudeof W₂ ^((k))(i,j), or a phase of W₂ ^((k))(i,j).

Based on that the vector V_(i,j) corresponds to W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) and that the vector D_(i,j) and thematrix F_(i,j) satisfy V_(i,j)=F_(i,j)×D_(i,j), the P_(i,j) elements inthe vector D_(i,j) are the finally reported limited quantity ofelements. In this case, the first indication information is used tospecifically indicate the quantity of these reported elements. In thiscase, the indication manner may specifically include but is not limitedto the following indication manners:

In a first manner, a quantity of elements in each vector D_(i,j)reported in the second indication information is indicated.

For example, as described above, the P_(i,j) elements in each vectorD_(i,j) are finally reported. In this case, the quantity of the elementsindicated by the second indication information may be the quantity ofthe elements in each vector D_(i,j), that is, P_(i,j), and (i,j)∈S. S isa nonempty subset of a set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . ,R})}.

Alternatively, in another feasible implementation scenario, an elementwith a largest value in the P_(i,j) elements in each vector D_(i,j) maybe separately reported. In this case, the quantity of the elementsindicated by the second indication information may be a quantity ofelements other than the separately reported element with the largestvalue in each vector D_(i,j), and may be specifically represented as:P_(i,j)−1, where (i,j)∈S. S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}, and 1 represents theseparately reported element with the largest value.

In addition, in another possible implementation scenario, if z elementswhose values rank top in the P_(i,j) elements in each vector D_(i,j) areseparately reported, the quantity of the elements indicated by thesecond indication information may be a quantity of elements other thanthe separately reported z elements in each vector D_(i,j), and may berepresented as: P_(i,j)−z, where (i,j)∈S. S is a nonempty subset of aset {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}, and z representsthe separately reported plurality of elements.

The set S in this application indicates value ranges of i and j in thevector D_(i,j) that needs to be reported by the terminal device. A sameconcept is used for a subsequent set S. Details are not described again.It should be noted that each matrix of the matrices W₂ ⁽¹⁾, W₂ ⁽²⁾, . .. , and W₂ ^((K)) is a matrix with L rows and R columns. However, in theK L×R matrices, amplitudes of some elements are 0, and the terminaldevice may not report D_(i,j) corresponding to the element whoseamplitude is 0. Therefore, values of i and j are a nonempty subset ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. A value set of(x,y) in {(x,y)|(x∈{1, 2, . . . , L}, y∈{1,2, . . . , R})}) is (1,1),(1,2), . . . , (1,R), (2,1), (2,2), . . . , (2,R), . . . , (L, 1), (L,2), . . . , and (L,R).

For example, Table 2 is used as an example, and the second indicationinformation indicates two vectors D_(1,1) and D_(3,1). The first vectorD_(1,1) includes two elements: y_(1,1) ⁽¹⁾ and y_(1,1) ⁽²⁾, and aquantity P_(1,1) of the elements in the vector D_(1,1) is 2. The secondvector D_(3,1) includes one element: y_(3,1) ⁽⁴⁾, and a quantity P_(3,1)of the element in the vector D_(3,1) is 1.

In this case, the first indication information may separately indicatethe quantities of the elements in the two vectors D_(1,1) and D_(3,1):2and 1. Alternatively, if an element with a largest value is separatelyreported in each vector, the first indication information may be used toseparately indicate a quantity of elements other than the separatelyreported elements with the largest value in the two vectors D_(1,1) andD_(3,1):1 (2−1=1) and 0 (1−1=0).

A quantity of elements in each vector D_(i,j) can be determined in amanner of separately reporting each vector D_(i,j), so that the basestation demodulates each vector D_(i,j) after receiving the thirdindication information.

In a second manner, a quantity of all elements reported in the secondindication information is indicated.

In this case, the quantity of the elements indicated by the secondindication information may be a sum of quantities of all elements in thevector D_(i,j). The quantity may be specifically represented asΣ_((i,j)∈S)P_(i,j), where S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

Alternatively, in another feasible implementation scenario, an elementwith a largest value in the P_(i,j) elements in each vector D_(i,j) maybe separately reported. In this case, the quantity of the elementsindicated by the second indication information may be a sum ofquantities of elements other than the separately reported element withthe largest value in the vector D_(i,j), and may be specificallyrepresented as: Σ_((i,j)∈S)(P_(i,j)−1), where S is a nonempty subset ofa set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}, and 1 representsthe separately reported element with the largest value.

In addition, in another possible implementation scenario, if z elementswhose values rank top in the P_(i,j) elements in each vector D_(i,j) areseparately reported, when the third indication information is generated,the quantity of the elements indicated by the second indicationinformation is a sum of quantities of elements other than the separatelyreported z elements in the vector D_(i,j), and may be specificallyrepresented as: Σ_((i,j)∈S)(P_(i,j)−z), where S is a nonempty subset ofa set {(x,y)|(x∈{1,2, . . . , L}, y∈{1 2, . . . , R})}, and z representsthe separately reported plurality of elements.

Table 2 is still used as an example, and the second indicationinformation indicates two vectors D_(1,1) and D_(3,1). The first vectorD_(1,1) includes two elements: y_(1,1) ⁽¹⁾ and y_(1,1) ⁽²⁾, and aquantity P_(1,1) of the elements in the vector D_(1,1) is 2. The secondvector D_(3,1) includes one element: y_(3,1) ⁽⁴⁾, and a quantity P_(3,1)of the element in the vector D_(3,1) is 1.

In this case, the first indication information is used to indicate thata total quantity of elements in the two vectors D_(1,1) and D_(3,1) is 3(2+1=3). Alternatively, if an element with a largest value is separatelyreported in each vector, the first indication information may be used toindicate a total quantity of elements other than the separately reportedelements with the largest value in the two vectors D_(i,j):1 (1+0=1).

Reporting the total quantity can assist the network device (the basestation) in demodulating the part 2 CSI, and can further effectivelyreduce a reporting amount of the terminal device.

In a third manner, the quantity of the elements reported in the secondindication information is indicated according to a (k^(th)) layer.

In this case, the quantity of the elements indicated by the secondindication information includes P_(q), where P_(q) is a sum of thequantity P_(i,j) of the elements when j=q is given:P_(q)=Σ_(j=q and (i,j)∈S)P_(i,j), and S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

For example, Table 2 is still used as an example, and the secondindication information indicates three vectors D_(1,1), D_(3,1), andD_(1,2). The first vector D_(1,1) includes two elements: y_(1,1) ⁽¹⁾ andy_(1,1) ⁽²⁾, and a quantity P_(1,1) of the elements in the vectorD_(1,1) is 2. The second vector D_(3,1) includes one element: y_(3,1)⁽⁴⁾, and a quantity P_(3,1) of the element in the vector D_(3,1) is 1.The third vector D_(1,2) includes four elements: y_(1,2) ⁽¹⁾, y_(1,2)⁽²⁾, y_(1,2) ⁽⁴⁾, and y_(1,2) ⁽⁶⁾, and a quantity P_(1,2) of theelements in the vector D_(1,2) is 4.

In this case, the first indication information may be used to indicatethat a total quantity of elements reported at a given data layer whosesequence number is 1 is 3, and be used to indicate that a total quantityof elements reported at a given data layer whose sequence number is 2 is4.

In addition, if the foregoing implementation scenario of separatelyreporting one element with a largest value or a plurality of elementswith a relatively large value is involved, a quantity of separatelyreported elements is further removed from the elements reported at eachlayer, and then a quantity of remaining elements is summed and reported.For example, if one element with a largest value is separately reported,the quantity P_(q) of the elements indicated by the second indicationinformation is a sum of the quantity P_(i,j) of the elements when j=q isgiven: P_(q)=Σ_(j=q and (i,j)∈S)(P_(i,j)−1), and S is a nonempty subsetof the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

In this embodiment of this application, the foregoing three indicationmanners of the first indication information may be used separately, ormay be used in a combination manner of at least two indication manners.The combination manner of the foregoing indication manners means that atleast two of the foregoing information are reported. For example, thefirst indication information may include P_(i,j) and Σ_((i,j)∈S)P_(i,j),that is, the first indication information may be used to indicate thequantity of the elements in each vector D_(i,j), or may be used toindicate the sum of quantities of all the elements in the vectorD_(i,j). Other combinations are not exhaustively listed here.

It should be noted that the hierarchical reporting manner in theforegoing third manner is a preferred implementation, and this helps thebase station demodulate data of each layer after receiving the thirdindication information. In addition, in specific implementation,reporting may alternatively be performed in a non-hierarchical manner,that is, reporting is performed in the foregoing first manner and/orsecond manner.

In addition, in specific implementation, considering that the secondindication information may be used to indicate a plurality of vectorsD_(i,j), for ease of processing, in a feasible implementation scenario,the method may further include the following step:

The terminal device sends sixth indication information, where the sixthindication information is used to indicate a quantity of the vectorsD_(i,j), where (i,j)∈S or (i,j)∈S and j=q are satisfied, and S is anonempty subset of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . ,R})}. The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . ,R})} is described in the foregoing paragraph.

This implementation may be used in combination with any indicationmanner of the first indication information. For example, the firstindication information is used to indicate the quantity P_(i,j) of theelements in the vector D_(i,j), and the sixth indication information isused to indicate the quantity of the vectors D_(i,j). In this case,Σ_((i,j)∈S)P_(i,j) may be obtained through the quantity P_(i,j) of theelements in the vector D_(i,j) and the quantity of the vectors D_(i,j).

In specific implementation, the sixth indication information and thethird indication information may be sent simultaneously. In addition, ina preferred implementation scenario, if the third indication informationis the CSI, the sixth indication information may be carried in the part1 CSI in the third indication information. In this case, the terminaldevice needs to send only one piece of third indication information.

In other words, in a possible implementation, the sixth indicationinformation is placed in the first part of the CSI (the part 1 CSI), andthe first indication information and the second indication informationare placed in the second part of the CSI (the part 2 CSI), where thesixth indication information is used to indicate a quantity of P_(i,j)in the first indication information. The first indication informationmay include a bitmap. The bitmap is used to determine positions ofelements in D_(i,j) in all sample points of a transform domain, orpositions of frequency-domain sub-bands determined by the terminaldevice.

In addition, for a specific implementation scenario of CSI compression,this application provides the following two feasible CSI compressionsolutions.

In a first CSI compression solution, the terminal device reports only aninflection point of each coefficient in frequency domain based on aposition of each coefficient in W₂ ^((k)) in frequency domain.

In this case, according to different representation meanings of thematrix V_(i,j) and that the vector D_(i,j) and the matrix F_(i,j)satisfy V_(i,j)=F_(i,j)×D_(i,j), the P_(i,j) elements in the vectorD_(i,j) indicated in the second indication information may have at leastthe following representation relationships:

the P_(i,j) elements in the vector D_(i,j) are P_(i,j) elements in W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), and the matrixF_(i,j) is used to obtain W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j) based on the P_(i,j) elements in the vector D_(i,j); or

the P_(i,j) elements in the vector D_(i,j) are phases of P_(i,j)elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), andthe matrix F_(i,j) is used to obtain the phases of W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j) elements inthe vector D_(i,j); or

the P_(i,j) elements in the vector D_(i,j) are amplitudes of P_(i,j)elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), andthe matrix F_(i,j) is used to obtain the amplitudes of W₂ ⁽¹⁾ (i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j) elements inthe vector D_(i,j).

For example, when the P_(i,j) elements in the vector D_(i,j) are thephases of the P_(i,j), elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , andW₂ ^((K))(i,j), FIG. 3 shows a curve of a frequency-domain relationshipbetween a phase (c_(i,j)) and a sub-band number of each vector D_(i,j).As shown in FIG. 3 , each vector D_(i,j) corresponds to one coefficient,that is, corresponds to one c_(i,j). For example, a curve 1 in FIG. 3shows that a coefficient c_(1,1) has inflection points at sub-bandnumbers 0, 3, 8, and 12. In this case, a vector D_(1,1) corresponding tothe coefficient c_(1,1) includes four elements in total: phases at thesub-band numbers 0, 3, 8, and 12. For another example, a curve 2 in FIG.3 shows that a coefficient c_(2,1) has inflection points at sub-bandnumbers 0, 4, 9, and 12. In this case, a vector D_(2,1) corresponding tothe coefficient c_(2,1) includes four elements in total: phases at thesub-band numbers 0, 4, 9, and 12. For another example, a curve 3 in FIG.3 shows that a coefficient c_(3,2) has inflection points at sub-bandnumbers 0, 8, and 12. In this case, a vector D_(3,2) corresponding tothe coefficient c_(3,2) includes three elements in total: phases at thesub-band numbers 0, 6, and 12.

In the foregoing precoding matrix indication solution, based on areported element that is of each coefficient and that is located at aninflection point, another element that is not reported and that is ofthe coefficient can be conveniently obtained based on a linearrelationship. Therefore, only a limited quantity of elements that arelocated at inflection points and that are in a curve of afrequency-domain relationship are used to represent the coefficient, andnot all elements of the coefficient need to be reported. This canfurther greatly reduce an amount of data reported by the terminaldevice.

In this implementation, the matrix F_(i,j) is used to obtain the matrixV_(i,j) based on the P_(i,j) elements in the vector D_(i,j). In thiscase, the matrix F_(i,j) may be an interpolation matrix, and is mainlyused to obtain a precoding matrix (or an amplitude or a phase of theprecoding matrix) on each sub-band by performing interpolation on theelements in the vector D_(i,j).

In this embodiment of this application, the following method is furtherprovided:

The terminal device sends fourth indication information, where thefourth indication information is used to indicate frequency-domainpositions of the P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . ,and W₂ ^((K))(i,j) that correspond to the P_(i,j) elements in D_(i,j).

Using the curve 1 shown in FIG. 3 as an example, the vector D_(1,1)corresponding to the curve 1 includes four elements in total, which arethe phases at 0, 3, 8, and 12. The second indication information in thethird indication information may include phase values of the fourelements included in the vector D_(1,1), and the first indicationinformation may indicate that a quantity of the elements indicated bythe vector D_(1,1) is 4. In addition, a sub-band number (0, 3, 8, or 12)corresponding to each element may be further indicated through thefourth indication information.

In specific implementation, the fourth indication information and thethird indication information may be sent simultaneously. In addition, ina preferred implementation scenario, if the third indication informationis the CSI, the fourth indication information may be carried in the part2 CSI in the third indication information. In this case, the terminaldevice needs to send only one piece of third indication information.

In addition, in this implementation, the third indication informationmay further include the foregoing sixth indication information. In thiscase, the sixth indication information is specifically used to indicatea quantity of coefficients reported in FIG. 3 .

In a second CSI compression solution, the terminal device processes eachcoefficient in W₂ ^((k)), and separately selects a limited quantity ofelements from each processed coefficient for reporting. Transformprocessing in this embodiment of this application may include but is notlimited to transform processing from a frequency domain to a timedomain, or cosine-related transform processing.

In this case, P_(i,j) vectors of the matrix F_(i,j) are orthogonal toeach other. Specifically, the matrix F_(i,j) may be:

P_(i,j) columns of a discrete Fourier transform (DFT) matrix; or

P_(i,j) columns of an inverse discrete Fourier transform (IDFT) matrix;or

P_(i,j) columns of a discrete cosine transform (DCT) matrix; or

P_(i,j) columns of an inverse discrete cosine transform (IDCT) matrix.

In this case, the precoding matrix indication method provided in thisapplication further includes the following step:

The terminal device sends fifth indication information, where the fifthindication information is used to indicate the matrix F_(i,j). In apossible implementation, the fifth indication information is used toindicate P_(i,j) columns of a transform matrix, and the transform matrixincludes but is not limited to the DFT matrix, the IDFT matrix, the DCTmatrix, and the IDFT matrix.

In specific implementation, the fifth indication information and thethird indication information may be sent simultaneously. In addition, ina preferred implementation scenario, if the third indication informationis the CSI, the fifth indication information may be carried in the part2 CSI in the third indication information. In this case, the terminaldevice needs to send only one piece of third indication information.

Specifically, the following uses an example in which the matrix F_(i,j)is an IDFT matrix for specific description. Referring to Table 2 andFIG. 4 , FIG. 4 shows a curve of a time-domain relationship obtainedafter IDFT transform is performed on coefficients in W₂ ^((k)). In FIG.4 , in each transform, Y_(i,j) in time domain corresponds to onetime-domain relationship curve. The first indication information is usedto indicate some time-domain sample points in each time-domainrelationship curve. These time-domain sample points are circled in FIG.4 , and a total quantity of these time-domain sample points in FIG. 4 isidentified as N2, where N2 may be a total quantity of sample points ofall coefficients in W₂ ^((k)) in time domain, or may be a total quantityof time-domain sample points of all coefficients at each layer in W₂^((k)). A quantity of time-domain sample points reported in eachcoefficient may be the same or different, and the reported time-domainsample points may be selected based on a preset condition as required ordetermined by processing personnel through processing. This is notparticularly limited in this application. For example, a curve 4corresponding to a coefficient Y_(1,1) includes four time-domain samplepoints that need to be reported in total. In this case, the secondindication information is used to indicate the four time-domain samplepoints corresponding to the coefficient Y_(1,1), and the firstindication information is used to indicate that a quantity of thetime-domain sample points reported in the second indication informationis 4.

In a preferred implementation scenario, some time-domain sample pointsreported in each coefficient are a limited quantity of time-domainsample points with a relatively large value.

In addition, in this implementation, in addition to the quantity N2indicated by the first indication information, the third indicationinformation may further include the foregoing sixth indicationinformation. In this case, the sixth indication information isspecifically used to indicate a quantity of coefficients reported inFIG. 4 , that is, a quantity N1 shown in FIG. 4 .

For the two CSI compression manners shown in FIG. 3 and FIG. 4 , thisembodiment of this application further provides indication manners ofthe fourth indication information and the fifth indication information.The fourth indication information and the fifth indication informationmay be carried in the first indication information. For ease ofdescription, the following uses FIG. 4 and the fifth indicationinformation as an example to describe representation manners of thefourth indication information and the fifth indication information.

This embodiment of this application provides two manners of representingthe fifth indication information:

A first representation manner is a bitmap manner. In this case, for thefifth indication information and for each non-zero wideband amplitudecoefficient Y_(i,j), a position of a reported element in the coefficientmay be indicated through a bit group of one or more bits.

In a preferred implementation scenario, the first indication informationincludes one or more bitmaps, and each bitmap includes K bits, and isused to indicate position indexes of the P_(i,j) elements in the vectorD_(i,j). In this case, the fifth indication information is carried inthe first indication information.

In another possible implementation, a sample point of the transformdomain may be obtained in an oversampling manner. In this case, aquantity of sample points of the transform domain is greater than aquantity K of sub-bands. In this manner, each of the bitmaps included inthe first indication information includes J bits, to indicate positionsof the P_(i,j) elements in the vector D_(i,j) in J sample points of thetransform domain, where J>K.

With reference to FIG. 4 and the fifth indication information, in thiscase, a bit group corresponding to each coefficient Y_(i,j) may berepresented in Table 3.

TABLE 3 Coefficient Bit group corresponding to the coefficient Y_(1,1)[1 1 1 1 0 0 0 . . . 0] Y_(2,1) [0 1 0 1 1 0 0 . . . 0] . . . . . .Y_(L,R) [0 1 0 1 0 0 0 . . . 0]

A second representation manner is a combinatorial number manner.

FIG. 4 and the fifth indication information are still used as anexample. A quantity of reported elements corresponding to thecoefficient Y_(1,1) is 4, and positions of these reported elements maybe reported in the combinatorial number manner: Four sample points C_(N)⁴ are selected from N sample points. A quantity of reported elementscorresponding to the coefficient Y_(2,1) is 3, and positions of thesereported elements may be reported in the combinatorial number manner:Three sample points C_(N) ³ are selected from N sample points. Aquantity of reported elements corresponding to the coefficient Y_(L,R)is 2, and positions of these reported elements may be reported in thecombinatorial number manner: Two sample points C_(N) ² are selected fromN sample points.

It should be noted that when the fifth indication information isreported in the combinatorial number manner, because a quantity of bitsthat carry C_(N) ^(m) is related to m, but a value of m is not indicatedin the part 1 CSI, to resolve this problem, a zero padding manner may beused to fix a quantity of bits of the part 2 CSI. In this case, themethod further includes the following steps:

The terminal obtains combinatorial number information.

The terminal performs padding processing on the combinatorial numberinformation, to obtain padded combinatorial number information, wherethe padded combinatorial number information has a fixed quantity ofbits.

For example, if a quantity of bits used to carry an element position isfixed at log 2(C_(N) ⁴), for the coefficient Y_(1,1), 0 does not need tobe added; for the coefficient Y_(2,1), one bit whose value is 0 needs tobe added; and for the coefficient Y_(L,R), two bits whose values areboth 0 need to be added.

In addition to the precoding matrix indication method performed on aterminal side, this application further provides a method performed onthe terminal side.

FIG. 5 is a schematic interaction flowchart of a precoding matrixindication method in an application scenario of CSI reporting accordingto this application. As shown in FIG. 5 , the method includes thefollowing steps.

S502: A terminal device generates third indication information.

S504: The terminal device sends the third indication information to anetwork device.

S506: The network device receives the third indication information.

S508: The network device sends downlink data based on the thirdindication information.

It should be noted that, as described above, the third indicationinformation received by the network device may include first indicationinformation and second indication information. In addition, in somepossible implementation scenarios, at least one of fourth indicationinformation, fifth indication information, and sixth indicationinformation may be further included. Description of the third indicationinformation is the same as the foregoing content, and details are notdescribed again.

In addition, in a feasible onsite scenario, in the procedure shown inFIG. 5 , a network device side may further include the following method.

S501: The network device sends a channel state information referencesignal (CSI-Reference Signal, CSI-RS) to the terminal device.

In this implementation scenario, that the terminal device generates thethird indication information is triggered after the terminal devicereceives the CSI-RS sent by the network device. This is a possibleimplementation scenario, and is not intended to limit this application.

It may be understood that some or all of the steps or operations in theforegoing embodiment are merely examples. Other operations or variationsof various operations may be further performed in this embodiment ofthis application. In addition, the steps may be performed in a sequencedifferent from that presented in the foregoing embodiment, and not alloperations in the foregoing embodiment may need to be performed.

It may be understood that, in the foregoing embodiments, an operation ora step implemented by the terminal device may also be implemented by acomponent (for example, a chip or a circuit) that can be used in theterminal device, an operation or a step implemented by the core networknode may also be implemented by a component (for example, a chip or acircuit) that can be used in the core network node, and an operation ora step implemented by the network device may also be implemented by acomponent (for example, a chip or a circuit) that can be used in thenetwork device.

It may be understood that, in the foregoing embodiments, an operation ora step implemented by the terminal may also be implemented by acomponent (for example, a chip or a circuit) that can be used in theterminal, an operation or a step implemented by the core network nodemay also be implemented by a component (for example, a chip or acircuit) that can be used in the core network node, and an operation ora step implemented by the network device may also be implemented by acomponent (for example, a chip or a circuit) that can be used in thenetwork device.

FIG. 6 is a schematic structural diagram of a communications apparatus.The communications apparatus may be configured to implement the methodcorresponding to the network device, a method corresponding to aposition determining entity, a method corresponding to a terminal, or amethod corresponding to a target LMU described in the foregoing methodembodiments. For details, refer to the descriptions in the foregoingmethod embodiments.

The communications apparatus 600 may include one or more processors 610.The processor 610 may also be referred to as a processing unit, and mayimplement a specific control function. The processor 610 may be ageneral purpose processor, a dedicated processor, or the like.

In an optional design, the processor 610 may also store a firstinstruction, and the first instruction may be run by the processor, sothat the communications apparatus 600 performs the method thatcorresponds to the network device or the terminal device and that isdescribed in the foregoing method embodiments.

A processing element may be a general purpose processor, for example, acentral processing unit (CPU), or may be configured as one or moreintegrated circuits that perform the foregoing methods, for example, oneor more application-specific integrated circuits (ASIC), one or moremicroprocessors (digital signal processor, DSP), or one or more fieldprogrammable gate arrays (FPGA). A storage element may be one memory, ormay be a general term of a plurality of storage elements.

In another possible design, the communications apparatus 600 may includea circuit. The circuit may implement a sending, receiving, orcommunication function in the foregoing method embodiments.

Optionally, the communications apparatus 600 may include one or morememories 620, the memory 620 stores a second instruction or intermediatedata, and the second instruction may be run on the processor, so thatthe communications apparatus 600 performs the method described in theforegoing method embodiments. Optionally, the memory may further storeother related data. Optionally, the processor may also storeinstructions and/or data. The processor and the memory may be separatelydisposed, or may be integrated together.

Optionally, the communications apparatus 600 may further include atransceiver 630. The transceiver 630 may be referred to as a transceiverunit, a transceiver machine, a transceiver circuit, a transceiver, orthe like, and is configured to implement sending and receiving functionsof the communications apparatus.

In the communications apparatus 600, the processor 610, the memory 620,and the transceiver 630 are connected through a bus.

If the communications apparatus 600 is configured to implement anoperation corresponding to the terminal device in the embodiments shownin FIG. 2 and FIG. 5 , the processor may be configured to generate thirdindication information, and the transceiver may be further configured tosend the third indication information. The transceiver may furthercomplete another corresponding communication function. The processor isconfigured to complete a corresponding determining or control operation,and optionally, may further store corresponding instructions in thememory. For a specific processing manner of each component, refer torelated descriptions in the foregoing embodiments.

If the communications apparatus 600 is configured to implement anoperation corresponding to the network device in FIG. 5 , thetransceiver may receive the third indication information sent by theterminal device, and the processor may implement the step of sendingdownlink data based on the third indication information. The transceivermay further complete another corresponding communication function. Theprocessor is configured to complete a corresponding determining orcontrol operation, and optionally, may further store correspondinginstructions in the memory. For a specific processing manner of eachcomponent, refer to related descriptions in the foregoing embodiments.

The processor and the transceiver described in this application may beimplemented on an integrated circuit (IC), an analog IC, a radiofrequency integrated circuit RFIC, a hybrid signal IC, anapplication-specific integrated circuit (ASIC), a printed circuit board(PCB), an electronic device, or the like. The processor and thetransceiver may also be manufactured through various 1C technologies,for example, a complementary metal oxide semiconductor (CMOS), an N-typemetal oxide semiconductor (NMOS), a P-type metal oxide semiconductorPMOS), a bipolar junction transistor (BJT), a bipolar CMOS (BiCMOS),silicon germanium (SiGe), and gallium arsenide (GaAs).

Optionally, the communications apparatus may be an independent device ormay be a part of a relatively large device. For example, the device maybe:

(1) an independent integrated circuit IC, a chip, or a chip system orsubsystem;

(2) a set having one or more ICs, where optionally, the IC set may alsoinclude a storage component configured to store data and/orinstructions;

(3) an ASIC, for example, a modem (MSM);

(4) a module that can be embedded in another device;

(5) a receiver, a terminal, a cellular phone, a wireless device, ahandheld phone, a mobile unit, a network device, or the like; or

(6) another device or the like.

In addition, FIG. 7 is a schematic structural diagram of acommunications apparatus according to an embodiment of this application.As shown in FIG. 7 , the communications apparatus 700 includes aprocessing module 710 and a sending module 720. The processing module710 is configured to generate third indication information, where thethird indication information is used to indicate W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . ,and W₂ ^((K)), where W^((k)) is a precoding matrix in a k^(th)frequency-domain unit, W^((k)) satisfies W^((k))=W₁×W₂ ^((k)), W₁ is anN_(t)×L matrix, W₂ ^((k)) is an L×R matrix, 0<k≤K, and K is a quantityof frequency-domain units; the third indication information includessecond indication information and first indication information; thesecond indication information is used to indicate P_(i,j) elements in avector D_(i,j), where the vector D_(i,j) and a matrix F_(i,j) satisfyV_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j) corresponds to W₂ ⁽¹⁾(i,j),W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), W₂ ^((k))(i,j) is a complexnumber in an i^(th) row and a j^(th) column of the matrix W₂ ^((k)), andF_(i,j) is a K×P_(i,j) matrix, where 0<i≤L, 0<j≤R, and P_(i,j)<K; andthe first indication information is used to indicate a quantity of theelements indicated by the second indication information; and the sendingmodule 720 is configured to send the third indication information.

According to the solution provided in this embodiment, a quantity ofelements reported in the precoding matrix is reported, so that a networkdevice that receives the third indication information can decode CSIbased on the information, and a terminal device can dynamically adjustthe quantity of the reported elements based on a channel condition. Thisreduces resource overheads required for CSI reporting.

In a possible design, that the vector V_(i,j) corresponds to W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) includes: V_(i,j) is acolumn vector including W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j); or V_(i,j) is a column vector including amplitudes of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . and W₂ ^((K))(i,j); or V_(i,j) is a columnvector including phases of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j). The vector V_(i,j) may be represented as V_(i,j)=[α_(i,j) ¹. . . α_(i,j) ^(K)]^(T), where α_(i,j) ^(k) is W₂ ^((k))(i,j), or anamplitude of W₂ ^((k)) (i,j), or a phase of W₂ ^((k))(i,j).

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(i,j) or P_(i,j)−1, and(i,j)∈S, where S is a nonempty subset of a set {(x,y)|(x∈{1,2, . . . ,L}, y∈{1,2, . . . , R})}.

The set S represents value ranges of i and j in the vector D_(i,j) thatneeds to be reported by the terminal device. It should be noted thateach matrix of the matrices W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)) is amatrix with L rows and R columns. However, in the K L×R matrices,amplitudes of some elements are 0, and the terminal device may notreport D_(i,j) corresponding to the element whose amplitude is 0.Therefore, values of i and j are a nonempty subset of the set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. A value set of (x,y)in {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}) is (1,1), (1,2), .. . , (1,R), (2,1), (2,2), . . . , (2,R), . . . , (L, 1), (L, 2), . . ., and (L, R).

According to the solution provided in this embodiment, a quantity ofelements in each vector D_(i,j) is reported, so that the quantity of thereported elements in the precoding matrix is indicated, thereby avoidingabnormal data transmission.

In a possible design, the quantity of the elements indicated by thesecond indication information includes: Σ_((i,j)∈S)P_(i,j) orΣ_((i,j)∈S)(P_(i,j)−1), where S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. According to the solutionprovided in this embodiment, a total quantity of the reported elementsin the precoding matrix is directly indicated, so that an amount of datareported by the terminal device can be reduced on a basis that thenetwork device can demodulate the CSI.

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(q), where P_(q) is a sum ofthe quantity P_(i,j) of the elements when j=q is given:P_(q)=Σ_(j=q and (i,j)∈S)P_(i,j) orP_(q)=Σ_(j=q and (i,j)∈S)(P_(i,j)−1), and S is a nonempty subset of aset {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. In the solution provided inthis embodiment, each j corresponds to a layer of the precoding matrix,so that the solution is used by the terminal device to report a quantityof reported elements corresponding to each layer. This hierarchicalreporting manner helps improve a CSI demodulation rate of the networkdevice.

In a possible design, the P_(i,j) elements in the vector D_(i,j) areP_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j) elements inthe vector D_(i,j); or the P_(i,j) elements in the vector D_(i,j) arephases of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain the phases of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j)elements in the vector D_(i,j); or the P_(i,j) elements in the vectorD_(i,j) are amplitudes of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j),. . . , and W₂ ^((K))(i,j), and the matrix F_(i,j) is used to obtain theamplitudes of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) basedon the P_(i,j) elements in the vector D_(i,j).

In this case, the sending module 720 is further configured to sendfourth indication information, where the fourth indication informationis used to indicate frequency-domain positions of the P_(i,j) elementsin W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) that correspondto the P_(i,j) elements in the vector D_(i,j).

According to the solution provided in this embodiment, not allcoefficients in W₂ ^((k)) need to be reported, and only an element at aninflection point that can represent a frequency-domain position of W₂^((k)) needs to be reported, thereby greatly reducing an amount of datareported by the terminal device.

In another possible design, P_(i,j) vectors of the matrix F_(i,j) areorthogonal to each other.

In this case, the sending module 720 is further configured to send fifthindication information, where the fifth indication information is usedto indicate the matrix F_(i,j).

According to the solution provided in this embodiment, matrixtransformation may be performed on coefficients in frequency domain, anda limited quantity of sample points with a relatively large value areselected, from results obtained after the matrix transformation, forreporting. In this way, the amount of data reported by the terminaldevice is reduced.

In another possible design, the sending module 720 is further configuredto send sixth indication information, where the sixth indicationinformation is used to indicate a quantity of the vectors D_(i,j), where(i,j)∈S or i,j satisfy (i,j)∈S and j=k, and S is a nonempty subset ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. The meaning ofthe set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})} is described inthe foregoing paragraph.

In another possible design, the first indication information includesone or more bitmaps; and each bitmap is used to indicate positions ofthe P_(i,j) elements in the vector D_(i,j).

In this embodiment, the first indication information includes onebitmap, so that the bitmap is used to indicate position information ofelements in all reported vectors D_(i,j) in K positions. Alternatively,the first indication information includes R bitmaps, and the bitmaps areused to indicate position information, in K positions, of elements invectors D_(i,j) whose value of j is 1, 2, . . . , or R in all reportedvectors D_(i,j). Alternatively, the first indication informationincludes L×R or (L−1)×R bitmaps, and the bitmaps are used to indicateposition information, in K positions, of an element that is in D_(i,j)and that corresponds to each element in W₂ or each element other than anelement corresponding to a largest amplitude in each column of W₂.

According to the solution provided in this embodiment, when the quantityof the reported elements is indicated, a position of the reportedelement may be indicated, and the position of the reported element doesnot need to be indicated in another manner. This manner has relativelyhigh flexibility and scalability.

In another possible design, the third indication information is channelstate information CSI, and the CSI includes: a first part, part 1 CSI,including the first indication information, a rank indicator RI, and achannel quality indicator CQI that corresponds to a first codeword; anda second part, part 2 CSI, including the second indication information,where the part 1 CSI and the part 2 CSI are independently encoded. Inthis way, the part 1 CSI may indicate a quantity of bits in the part 2CSI, so that the network device that receives the third indicationinformation can decode the CSI based on the information, therebyavoiding abnormal data transmission.

In addition, FIG. 8 is a schematic structural diagram of acommunications apparatus according to an embodiment of this application.As shown in FIG. 8 , the communications apparatus 800 includes areceiving module 810 and a processing module 820. The receiving module810 is configured to receive third indication information, where thethird indication information is used to indicate W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . ,and W₂ ^((K)), where W^((k)) is a precoding matrix in a k^(th)frequency-domain unit, W^((k)) satisfies W^((k))=W₁×W₂ ^((k)), W₁ is anN_(t)×L matrix, W₂ ^((k)) is an L×R matrix, 0<k≤K, and K is a quantityof frequency-domain units; the third indication information includessecond indication information and first indication information; thesecond indication information is used to indicate P_(i,j) elements in avector D_(i,j), where the vector D_(i,j) and a matrix F_(i,j) satisfyV_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j) corresponds to W₂ ⁽¹⁾(i,j),W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), W₂ ^((k))(i,j) is a complexnumber in an i^(th) row and a j^(th) column of the matrix W₂ ^((k)), andF_(i,j) is a K×P_(i,j) matrix, where 0<i≤L, 0<j≤R, and P_(i,j)<K; andthe first indication information is used to indicate a quantity of theelements indicated by the second indication information; and theprocessing module 820 is configured to send downlink data based on thethird indication information.

According to the solution provided in this embodiment, a quantity ofelements reported in the precoding matrix is reported, so that a networkdevice that receives the third indication information can decode CSIbased on the information, and a terminal device can dynamically adjustthe quantity of the reported elements based on a channel condition. Thisreduces resource overheads required for CSI reporting.

In a possible design, that the vector V_(i,j) corresponds to W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) includes: V_(i,j) is acolumn vector including W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j); or V_(i,j) is a column vector including amplitudes of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . and W₂ ^((K))(i,j); or V_(i,j) is a columnvector including phases of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j). The vector V_(i,j) may be represented as V_(i,j)=[α_(i,j) ¹. . . α_(i,j) ^(K)]^(T), where α_(i,j) ^(k) is W₂ ^((k))(i,j), or anamplitude of W₂ ^((k))(i,j), or a phase of W₂ ^((k))(i,j).

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(i,j) or P_(i,j)−1, and(i,j)∈S, where S is a nonempty subset of a set {(x,y)|(x∈{1,2, . . . ,L}, y∈{1,2, . . . , R})}.

The set S represents value ranges of i and j in the vector D_(i,j) thatneeds to be reported by the terminal device. It should be noted thateach matrix of the matrices W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)) is amatrix with L rows and R columns. However, in the K L×R matrices,amplitudes of some elements are 0, and the terminal device may notreport D_(i,j) corresponding to the element whose amplitude is 0.Therefore, values of i and j are a nonempty subset of the set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}. A value set of (x,y)in {(x,y)|(x∈{1, 2, . . . , L}, y∈{1,2, . . . , R})}) is (1,1), (1,2), .. . , (1,R), (2,1), (2,2), . . . , (2,R), . . . , (L,1), (L,2), . . . ,and (L,R).

According to the solution provided in this embodiment, a quantity ofelements in each vector D_(i,j) is reported, so that the quantity of thereported elements in the precoding matrix is indicated, thereby avoidingabnormal data transmission.

In a possible design, the quantity of the elements indicated by thesecond indication information includes: Σ_((i,j)∈S)P_(i,j) orΣ_((i,j)∈S)(P_(i,j)−1), where S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1, 2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. According to the solutionprovided in this embodiment, a total quantity of the reported elementsin the precoding matrix is directly indicated, so that an amount of datareported by the terminal device can be reduced on a basis that thenetwork device can demodulate the CSI.

In a possible design, the quantity of the elements indicated by thesecond indication information includes P_(q), where P_(q) is a sum ofthe quantity P_(i,j) of the elements when j=q is given:P_(q)=Σ_(j=q and (i,j)∈S)P_(i,j) orP_(q)=Σ_(j=q and (i,j)∈S)(P_(i,j)−1), and S is a nonempty subset of aset {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}.

The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . , R})}is described in the foregoing paragraph. In the solution provided inthis embodiment, each j corresponds to a layer of the precoding matrix,so that the solution is used by the terminal device to report a quantityof reported elements corresponding to each layer. This hierarchicalreporting manner helps improve a CSI demodulation rate of the networkdevice.

In a possible design, the P_(i,j) elements in the vector D_(i,j) areP_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j) elements inthe vector D_(i,j); or the P_(i,j) elements in the vector D_(i,j) arephases of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j), and the matrix F_(i,j) is used to obtain the phases of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) based on the P_(i,j)elements in the vector D_(i,j); or the P_(i,j) elements in the vectorD_(i,j) are amplitudes of P_(i,j) elements in W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j),. . . , and W₂ ^((K))(i,j), and the matrix F_(i,j) is used to obtain theamplitudes of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) basedon the P_(i,j) elements in the vector D_(i,j).

In this case, the receiving module 810 is further configured to receivefourth indication information, where the fourth indication informationis used to indicate frequency-domain positions of the P_(i,j) elementsin W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) that correspondto the P_(i,j) elements in the vector D_(i,j).

According to the solution provided in this embodiment, not allcoefficients in W₂ ^((k)) need to be reported, and only an element at aninflection point that can represent a frequency-domain position of W₂^((k)) needs to be reported, thereby greatly reducing an amount of datareported by the terminal device.

In another possible design, P_(i,j) vectors of the matrix F_(i,j) areorthogonal to each other.

In this case, the receiving module 810 is further configured to receivefifth indication information, where the fifth indication information isused to indicate the matrix F_(i,j).

According to the solution provided in this embodiment, matrixtransformation may be performed on coefficients in frequency domain, anda limited quantity of sample points with a relatively large value areselected, from results obtained after the matrix transformation, forreporting. In this way, the amount of data reported by the terminaldevice is reduced.

In another possible design, the receiving module 810 is furtherconfigured to receive sixth indication information, where the sixthindication information is used to indicate a quantity of the vectorsD_(i,j), where (i,j)∈S or (i,j)∈S and j=q are satisfied, and S is anonempty subset of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . ,R})}. The meaning of the set {(x,y)|(x∈{1,2, . . . , L}, y∈{1,2, . . . ,R})} is described in the foregoing paragraph.

In another possible design, the first indication information includesone or more bitmaps; and each bitmap is used to indicate positions ofthe P_(i,j) elements in the vector D_(i,j).

In this embodiment, the first indication information includes onebitmap, so that the bitmap is used to indicate position information ofelements in all reported vectors D_(i,j) in K positions. Alternatively,the first indication information includes R bitmaps, and the bitmaps areused to indicate position information, in K positions, of elements invectors D_(i,j) whose value of j is 1, 2, . . . , or R in all reportedvectors D_(i,j). Alternatively, the first indication informationincludes L×R or (L−1)×R bitmaps, and the bitmaps are used to indicateposition information, in K positions, of an element that is in D_(i,j)and that corresponds to each element in W₂ or each element other than anelement corresponding to a largest amplitude in each column of W₂.

According to the solution provided in this embodiment, when the quantityof the reported elements is indicated, a position of the reportedelement may be indicated, and the position of the reported element doesnot need to be indicated in another manner. This manner has relativelyhigh flexibility and scalability.

In another possible design, the third indication information is channelstate information CSI, and the CSI includes: a first part, part 1 CSI,including the first indication information, a rank indicator RI, and achannel quality indicator CQI that corresponds to a first codeword; anda second part, part 2 CSI, including the second indication information,where the part 1 CSI and the part 2 CSI are independently encoded. Inthis way, the part 1 CSI may indicate a quantity of bits in the part 2CSI, so that the network device that receives the third indicationinformation can decode the CSI based on the information, therebyavoiding abnormal data transmission.

It should be understood that division into the foregoing modules of thecommunications apparatus shown in FIG. 7 and FIG. 8 is merely logicalfunction division. In actual implementation, all or some of the modulesmay be integrated into one physical entity, or may be physicallyseparated. In addition, all of the modules may be implemented in a formof software invoked by a processing element or in a form of hardware.Alternatively, some of the modules may be implemented in a form ofsoftware invoked by a processing element, and some of the modules may beimplemented in a form of hardware. For example, the processing modulemay be an independently disposed processing element, or may beintegrated into a communications apparatus, for example, a chip of anetwork device for implementation. In addition, the processing modulemay be stored in a memory of the communications apparatus in a form of aprogram to be invoked by a processing element of the communicationsapparatus to perform a function of each of the foregoing modules.Implementations of other modules are similar. In addition, all or someof the modules may be integrated together, or may be implementedindependently. The processing element described herein may be anintegrated circuit with a signal processing capability. In animplementation process, steps in the method or the modules can beimplemented by using a hardware integrated logic circuit in theprocessing element, or by using instructions in a form of software.

For example, the foregoing modules may be one or more integratedcircuits configured to implement the foregoing methods, for example, oneor more ASICs, one or more DSPs, or one or more field programmable gatearrays (FPGA). For another example, when one of the foregoing modules isimplemented in a form of scheduling a program by a processing element,the processing element may be a general purpose processor, for example,a central processing unit (CPU) or another processor that can invoke theprogram. For still another example, the modules may be integratedtogether, and implemented in a form of a system-on-a-chip (SOC).

An embodiment of this application further provides a communicationsapparatus, and the communications apparatus may be a terminal device, ormay be a chip in a terminal device. The communications apparatus may beconfigured to perform an action performed by the terminal device in theforegoing method embodiments.

An embodiment of this application further provides a communicationsapparatus, and the communications apparatus may be a terminal device ora circuit. The communications apparatus may be configured to perform anaction performed by the terminal device in the foregoing methodembodiments.

When the communications apparatus is a terminal device, FIG. 9 is asimplified schematic structural diagram of a terminal device. For easeof understanding and convenience of figure illustration, an example inwhich the terminal device is a mobile phone is used in FIG. 9 . As shownin FIG. 9 , the terminal device includes a processor, a memory, a radiofrequency circuit, an antenna, and an input/output apparatus. Theprocessor is mainly configured to: process a communications protocol andcommunication data, control the terminal device, execute a softwareprogram, process data of the software program, and the like. The memoryis mainly configured to store the software program and the data. Theradio frequency circuit is mainly configured to: perform conversionbetween a baseband signal and a radio frequency signal, and process theradio frequency signal. The antenna is mainly configured to receive andsend a radio frequency signal in an electromagnetic wave form. Theinput/output apparatus, such as a touchscreen, a display screen, and akeyboard, is mainly configured to receive data input by a user andoutput data to the user. It should be noted that some types of terminaldevices may not have the input/output apparatus.

When data needs to be sent, after performing baseband processing on theto-be-sent data, the processor outputs a baseband signal to the radiofrequency circuit. After performing radio frequency processing on thebaseband signal, the radio frequency circuit sends the radio frequencysignal in an electromagnetic wave form via the antenna. When data issent to the terminal device, the radio frequency circuit receives aradio frequency signal via the antenna, converts the radio frequencysignal into a baseband signal, and outputs the baseband signal to theprocessor. The processor converts the baseband signal into data, andprocesses the data. For ease of description, FIG. 9 shows only onememory and processor. In an actual terminal device product, there may beone or more processors and one or more memories. The memory may also bereferred to as a storage medium, a storage device, or the like. Thememory may be disposed independent of the processor, or may beintegrated with the processor. This is not limited in this embodiment ofthis application.

In this embodiment of this application, the antenna and the radiofrequency circuit that have receiving and sending functions may beconsidered as a transceiver unit of the terminal device, and theprocessor that has a processing function may be considered as aprocessing unit of the terminal device. As shown in FIG. 9 , theterminal device includes a transceiver unit 910 and a processing unit920. The transceiver unit may also be referred to as a transceiver, atransceiver machine, a transceiver apparatus, or the like. Theprocessing unit may also be referred to as a processor, a processingboard, a processing module, a processing apparatus, or the like.Optionally, a component that is in the transceiver unit 910 and that isconfigured to implement a receiving function may be considered as areceiving unit, and a component that is in the transceiver unit 910 andthat is configured to implement a sending function may be considered asa sending unit. In other words, the transceiver unit 910 includes thereceiving unit and the sending unit. The transceiver unit sometimes mayalso be referred to as a transceiver machine, a transceiver, atransceiver circuit, or the like. The receiving unit may also besometimes referred to as a receiving machine, a receiver, a receivercircuit, or the like. The sending unit may also be sometimes referred toas a transmitting machine, a transmitter, a transmitter circuit, or thelike.

It should be understood that the transceiver unit 910 is configured toperform a sending operation and a receiving operation on a terminal sidein the foregoing method embodiments, and the processing unit 920 isconfigured to perform an operation other than the receiving/sendingoperation of the terminal device in the foregoing method embodiments.

For example, in an implementation, the transceiver unit 910 isconfigured to perform the sending operation on the terminal side in S204in FIG. 2 , and/or the transceiver unit 910 is further configured toperform another receiving and sending step on the terminal side in theembodiments of this application. The processing unit 920 is configuredto perform the step on the terminal side in S202 in FIG. 2 , and/or theprocessing unit 920 is further configured to perform another processingstep on the terminal side in the embodiments of this application.

When the communications apparatus is a chip, the chip includes atransceiver unit and a processing unit. The transceiver unit may be aninput/output circuit or a communications interface. The processing unitis a processor, a microprocessor, or an integrated circuit integrated onthe chip.

When the communications apparatus in this embodiment is a terminaldevice, reference may be made to a device shown in FIG. 10 . In anexample, the device can implement a function similar to that of theprocessor 610 in FIG. 6 . In FIG. 10 , the device includes a processor1010, a data sending processor 1020, and a data receiving processor1030. The processor 1010 in the foregoing embodiment may be theprocessor 1010 in FIG. 10 , and completes a corresponding function. Thedata receiving processor 1030 in the foregoing embodiment may be thedata sending processor 1020 and/or the data receiving processor 1030 inFIG. 10 . Although FIG. 10 shows a channel encoder and a channeldecoder, it may be understood that these modules are merely examples,and do not constitute limitative descriptions of this embodiment.

FIG. 11 shows another form of this embodiment. A processing apparatus1100 includes modules such as a modulation subsystem, a centralprocessing subsystem, and a peripheral subsystem. The communicationsapparatus in this embodiment may be used as the modulation subsystem inthe processing apparatus 1100. Specifically, the modulation subsystemmay include a processor 1103 and an interface 1104. The processor 1103completes a function of the processor 610, and the interface 1104completes a function of the transceiver 630. In another variation, themodulation subsystem includes a memory 1106, a processor 1103, and aprogram that is stored in the memory 1106 and that can be run on theprocessor. When executing the program, the processor 1103 implements themethod on the terminal side in the foregoing method embodiments. Itshould be noted that the memory 1106 may be nonvolatile or volatile. Thememory 1106 may be located in the modulation subsystem, or may belocated in the processing apparatus 1100, provided that the memory 1106can be connected to the processor 1103.

In another form of this embodiment, a computer-readable storage mediumis provided. The computer-readable storage medium stores instructions.When the instructions are executed, the method on the terminal side inthe foregoing method embodiments is performed.

In another form of this embodiment, a computer program product thatincludes instructions is provided. When the instructions are executed,the method on the terminal side in the foregoing method embodiments isperformed.

In addition, an embodiment of this application further provides acomputer-readable storage medium. The computer-readable storage mediumstores a computer program. When the computer program is run on acomputer, the computer is enabled to perform the precoding matrixindication method in the foregoing embodiments.

In addition, an embodiment of this application further provides acomputer program product. The computer program product includes acomputer program. When the computer program is run on a computer, thecomputer is enabled to perform the method in the foregoing embodiments.

All or some of the foregoing embodiments may be implemented by usingsoftware, hardware, firmware, or any combination thereof. When softwareis used to implement the embodiments, the embodiments may be implementedcompletely or partially in a form of a computer program product. Thecomputer program product includes one or more computer instructions.When the computer program instructions are loaded and executed on acomputer, the procedure or functions according to this application areall or partially generated. The computer may be a general-purposecomputer, a dedicated computer, a computer network, or anotherprogrammable apparatus. The computer instructions may be stored in thecomputer-readable storage medium or may be transmitted from acomputer-readable storage medium to another computer-readable storagemedium. For example, the computer instructions may be transmitted from awebsite, computer, server, or data center to another website, computer,server, or data center in a wired (for example, a coaxial cable, anoptical fiber, or a digital subscriber line) or wireless (for example,infrared, radio, or microwave) manner. The computer-readable storagemedium may be any usable medium accessible by the computer, or a datastorage device, such as a server and a data center, integrating one ormore usable media. The usable medium may be a magnetic medium (forexample, a floppy disk, a hard disk, or a magnetic tape), an opticalmedium (for example, a DVD), a semiconductor medium (for example, asolid-state drive Solid State Disk), or the like.

The foregoing descriptions are merely specific implementations of thepresent invention, but are not intended to limit the protection scope ofthe present invention. Any variation or replacement readily figured outby a person skilled in the art within the technical scope disclosed inthe present invention shall fall within the protection scope of thepresent invention. Therefore, the protection scope of the presentinvention shall be subject to the protection scope of the claims.

The invention claimed is:
 1. A precoding matrix indication method for anetwork device, wherein the method comprises: receiving third indicationinformation, wherein the third indication information indicates W₂ ⁽¹⁾,W₂ ⁽²⁾, . . . , and W₂ ^((K)), wherein W^((k)) is a precoding matrix ina k^(th) frequency-domain unit, W^((k)) satisfies W^((k))=W₁×W₂ ^((k)),W₁ is an N_(t)×L matrix, W₂ ^((k)) is an L×R matrix, 0<k≤K, and K is aquantity of frequency-domain units, and L and R are integers, whereinthe third indication information comprises second indicationinformation, the second indication information indicates P_(i,j)elements in a vector D_(i,j), wherein the vector D_(i,j) and a matrixF_(i,j) satisfy V_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j) correspondsto W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), W₂ ^((k))(i,j)is a complex number in an i^(th) row and a j^(th) column of the matrixW₂ ^((k)), and F_(i,j) is a K×P_(i,j) matrix, where 0<i≤L, 0<j≤R, andP_(i,j)<k; and sending downlink data based on the third indicationinformation.
 2. The method according to claim 1, wherein the thirdindication information further comprises first indication information;the first indication information indicates a quantity of the elementsindicated by the second indication information.
 3. The method accordingto claim 1, wherein that the vector V_(i,j) corresponds to W₂ ⁽¹⁾(i,j),W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) comprises: V_(i,j) is a columnvector including W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j);or V_(i,j) is a column vector including amplitudes of W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j); or V_(i,j) is a column vectorincluding phases of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j).
 4. The method according to claim 1, wherein the quantity ofthe elements indicated by the second indication information comprisesΣ_((i,j)∈S)P_(i,j)or Σ_((i,j)∈S)(P_(i,j)−1), wherein S is a nonemptysubset of a set {(x,y)|(x∈{1,2, . . . , L}), y∈{1,2, . . . , R})}. 5.The method according to claim 1, wherein P_(i,j) vectors of the matrixF_(i,j) are orthogonal to each other.
 6. The method according to claim1, wherein the method further comprises: receiving fifth indicationinformation, wherein the fifth indication information indicates thematrix F_(i,j).
 7. The method according to claim 2, wherein the firstindication information comprises one or more bitmaps; and each bitmap ofthe one or more bitmaps indicates positions of the P_(i,j) elements inthe vector D_(i,j).
 8. The method according to claim 2, wherein thethird indication information is channel state information (CSI), and theCSI comprises: a first part (part 1) CSI, comprising the firstindication information, a rank indicator (RI), and a channel qualityindicator (CQI) that corresponds to a first codeword; and a second part(part 2) CSI, comprising the second indication information, wherein thepart 1 CSI and the part 2 CSI are independently encoded.
 9. Acommunications apparatus, wherein the communications apparatuscomprises: at least one processor; and one or more memories coupled tothe at least one processor and storing programming instructions forexecution by the at least one processor to cause the apparatus to:receive third indication information, wherein the third indicationinformation indicates W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , W₂ ^((K)), wherein W^((k))is a preceding matrix in a k^(th) frequency-domain unit, W^((k))satisfies W^((k))=W₁×W₂ ^((k)), W₁ is an N_(t) ×L matrix, W₂ ^((k)) isan L×R matrix, 0<k≤K, and K is a quantity of frequency-domain units, andL and R are integers; the third indication information comprises secondindication information and first indication information; the secondindication information indicates P_(i,j) elements in a vector D_(i,j),wherein the vector D_(i,j) and a matrix F_(i,j) satisfyV_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j) corresponds to W₂ ⁽¹⁾(i,j),W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j), W₂ ^((k))(i,j) is a complexnumber in an i^(th) row and a j^(th) column of the matrix W₂ ^((k)), andF_(i,j) is a K×P_(i,j) matrix, wherein 0<i≤L, 0<j≤R, and P_(i,j)<K; andthe first indication information indicates a quantity of the elementsindicated by the second indication information; and send downlink databased on t third indication information.
 10. The communicationsapparatus according to claim 9, wherein that the vector V_(i,u)corresponds to W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j)comprises: V_(i,j) is a column vector including W₂ ⁽¹⁾(i,j), W₂⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j); or V_(i,j) is a column vectorincluding amplitudes of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j); or V_(i,j) is a column vector including phases of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j).
 11. Thecommunications apparatus according to claim 9, wherein the quantity ofthe elements indicated by the second indication information comprisesΣ_((i,j)∈S)P_(i,j) or Σ_((i,j)∈S)(P_(i,j)−1), wherein S is a nonemptysubset of a set {(x, y)|x ∈{1,2, . . . , L}y ∈{1,2, . . . , R})}. 12.The communications apparatus according to claim 9, wherein P_(i,j)vectors of the matrix F_(i,j) are orthogonal to each other.
 13. Thecommunications apparatus according to claim 9, wherein the one or morememories store programming instructions for execution by the at leastone processor to cause the apparatus to: receive fifth indicationinformation, wherein the fifth indication information indicates thematrix F_(i,j).
 14. The communications apparatus according to claim 9,wherein the first indication information comprises one or more bitmaps;and each bitmap of the one or more bitmaps indicates positions of theP_(i,j 1) elements in the vector D_(i,j).
 15. The communicationsapparatus according to claim 9, wherein the third indication informationis channel state information (CSI), and the CSI comprises: a first part(part 1) CSI, comprising the first indication information, a rankindicator (RI), and a channel quality indicator (CQI) that correspondsto a first codeword; and a second part (part 2) CSI, comprising thesecond indication information, wherein the part 1 CSI and the part 2 CSIare independently encoded.
 16. A non-transitory computer-readablestorage medium coupled to at least one processor and storing programminginstructions for execution by the at least one processor, wherein theprogramming instructions instruct the at least one processor to: receivethird indication information, wherein the third indication informationindicates W₂ ⁽¹⁾, W₂ ⁽²⁾, . . . , and W₂ ^((K)), wherein W^((K)) is aprecoding matrix in a k^(th) frequency- domain unit, W^((k)) satisfiesW^((k))=W₁×W₂ ^((k)), W₁ is an N_(t)×L matrix, W₂ ^((k)) is an L×Rmatrix, 0<k≤K, and K is a quantity of frequency-domain units, and L andR are integers; the third indication information comprises secondindication information and first indication information; the secondindication information indicates P_(i,j) elements in a vector D_(i,j),wherein the vector D_(i,j) and a matrix F_(i,j) satisfyV_(i,j)=F_(i,j)×D_(i,j), the vector V_(i,j) corresponds to W₂ ⁽¹⁾(i,j),W₂ ⁽²⁾(i,j), . . . , and W₂ ^((k)), and F_(i,j) is a K×P_(i,j) matrix,wherein 0<i≤L, 0<j≤R, and P_(i,j)K; and the first indication informationindicates a quantity of the elements indicated by the second indicationinformation; and send downlink data based on the third indicationinformation.
 17. The non-transitory computer-readable storage mediumaccording to claim 16, wherein that the vector V_(i,j) corresponds to W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j) comprises: V_(i,j) isa column vector including W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂^((K))(i,j); or V_(i,j) is a column vector including amplitudes of W₂⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , and W₂ ^((K))(i,j); or V_(i,j) is acolumn vector including phases of W₂ ⁽¹⁾(i,j), W₂ ⁽²⁾(i,j), . . . , andW₂ ^((K))(i,j).
 18. The non-transitory computer-readable storage mediumaccording to claim 16 , wherein the quantity of the elements indicatedby the second indication information comprises Σ_((i,j)∈S)P_(i,j) orΣ_((i,j)∈S)(P_(i,j)−1) , wherein S is a nonempty subset of a set{(x,y)|(x∈{1,2, . . . , L}, y ∈{1,2, . . . , R})}.
 19. Thenon-transitory computer-readable storage medium according to claim 16,wherein P_(i,j) vectors of the matrix F_(i,j) are orthogonal to eachother.
 20. The non-transitory computer-readable storage medium accordingto claim 16, wherein the first indication information comprises one ormore bitmaps; and each bitmap of the one or more bitmaps indicatespositions of the P_(i,j) elements in the vector D_(i,j).